From Diablo Wiki
Cinematics or cut-scenes are movies seen in the game, or released as promotional tools, that tell the game story, introduce new characters, or just generally serve as promotion or advertising. Blizzard has a long history of producing high quality movies through their in-house Cinematics Team, and these have been included with every game they've released since WarCraft II.
 Diablo 3 Cinematics
During the development of Diablo III, Blizzard released three full CGI cinematics, and three class introduction cinematics which were produced machinima-style using the game engine.
 Full CGI Movies
- Cinematic: WWI 2008 was the first, released with Diablo 3's premiere at the Paris WWI event, June 2008. This cinematic introduces the game world, hints at the plot, and shows some great scenery.
- The Black Soulstone cinematic debuted at Blizzcon 2011 and offered the first preview of one of the full game cinematics. This movie will show after Act 2, setting up plot events in Act Three. Note that this is a slightly-edited version of the movie, with a few things removed to preserve plot spoilers.
- Diablo III Introduction cinematic debuted in December 2011. This is the full game opening cinematic which players will view before the action begins in Act One. It introduces Leah and Deckard Cain, shares extensive background history of Sanctuary, and leads into the opening action of the game, with the mystery of the falling star that crashes into the Tristram Cathedral.
 Class Intro Movies
These were produced in the game engine, machinima-style, and debuted with each of the final three classes, at Blizzcon in 2008, 2009, and 2010.
- Cinematic: Wizard was released at Blizzcon 2008. This machinima style movie introduced the Wizard character, and showed her marching boldly through the Tristram Cathedral, past scornful villagers, en route to a final battle with Leoric, the Skeleton King.
- Cinematic: Monk was released at Blizzcon 2009. This machinima style movie introduced the Monk character and showed him battling Cultists in Arcarnus, before a final battle against a disguised Morlu Caster.
- Cinematic: Demon Hunter was released at Blizzcon 2010. This one introduced the Demon Hunter, and made clear the growing expertise of the Blizzard cinematics guys with the machinima style of in-game movie making. (Though many fans found the dialogue painfully corny.) In the film the Demon Hunter finds signs of a massacre, tracks the one human survivor and defends her from another attack of demons, before recruiting her as a new Demon Hunter.
Though many fans requested them, Blizzard declined to retroactively create machinima-style introductory cinematics for the Barbarian and Witch Doctor as they thought it would be too much effort for little purpose.
Players will view short cinematic intro movies for all five classes, in the final game. These are created with voiceovers from the characters themselves, and feature 2D style animation similar to that of the "Deckard Cain's Journal comes to life" as seen in the full game intro cinematic.
 Final Game Cinematics
There will be extensive cinematics in the full game, approximately twenty minutes of them, divided up into multiple short films which will be viewed before the game, after each act, and after the final battle, much as they were in Diablo 2. Kevin Martens and Julian Love commented on that during a Blizzcon 2009 interview: 
- Diii.net: Can you comment on the cinematics? The overall length and presentation? When will players see them during the game, and how long will they run for?
- Kevin: That’s not really been decided, since they’re still a work in progress. Currently the plan is to show some at the beginning and end of each Act, but the exact structure isn’t yet finished.
- Diii.net: Any idea how long they’ll be in total? Comparable to D2?
- Kevin: We really don’t know yet, since all of the scripts aren’t finished.
- We're using cinematics to about the same level as Diablo II did.
- It's a difficult story to tell with cinematics because we basically have a main character who can't be in the cinematics. We've really focused on the ancillary characters - Their focus is always to be kind of implying the player's presence right outside the room on the other side of that door.
- We don't have a big focus on in-game cinematics. We try to tell our story through action, through questing, and through events. We do have a lot more scripted events, but we separate those from in-game cinematics in the fact that we don't pull control away from the player.
 In-Game Cinematics
The D3 Team considered including more cinematics in the game, using the in-game engine, as is done in Starcraft 2. This was ultimately rejected for various reasons, as detailed by Jay Wilson in August 2010. 
- The team debated implementing realtime-cutscenes using the game engine (as is done in Starcraft 2) but scrapped the idea since it would have been too much work. There are too many characters, too many NPCs, and with five classes, times two for each gender, plus 18 different armor sets/appearances.
 Cinematics vs. Machinima
The traditional, fully CG cinematics are animated short movies about the games. These are produced by the Blizzard cinematics team in much the way a movie company like Pixar creates their feature films, and while these movies originate from the same concept art and designs as the rest of the game, almost all of the artwork and environments are created from scratch for the films.
The newer type of "cinematic" that's been used extensively to promote World of Warcraft and now Diablo 3, is created with the game engine itself. This technique is known as Machinima, and players can make this type of movie themselves, simply by recording what their character sees as they play. The better fan-made movies are created with the assistance of third party tools, and include soundtracks, dialogue, and sometimes even original special effects and animations. One fine WoW example can be seen here.
Red vs. Blue, A fan-made series using the Halo game engine, has become a huge internet success, with episodes even being sold on DVD with the consent of game publisher Microsoft.
 D3 Machinima Confusion
The fact that players never have the "first person" view while playing Diablo 3 (unlike WoW machinima movies) is probably what's led to some of the confusion, and various members of the Diablo 3 team have repeatedly had to explain that those movies are not "true" cinematics. 
- Joystiq.com: Monk introduction cinematic was choppy in a few places, it looked a little rough. You know, usually Blizzard's cinematics are so gorgeous and everything looks like it's out of a CGI movie. Was that put together in-game? How did you guys create that?
- Leonard Boyarsky: Yeah, that's an in-game done by our AV team. We have two different ways of doing them. A lot of times when they announce patches for World of Warcraft, you'll notice that they'll do in-game ones as opposed to full-on cinematic ones. That's what that one was. Same with our Wizard one last time. They were developing that as we were developing a lot of his skills. I think they did a really good job with the limited tools that we allowed them to have at the time. [laughs] But I thought it was really cool, myself. But I know what you're saying.
- Yeah, there were a few times where you were like, "Oh, it's a little choppy" or some of the characters in the background looked all the same, you know. They're facing the same way, moving the same way.
- Kevin Martens: They didn't get the assets very early; they didn't have more time.
- Leonard: We'll take full responsibility for that. [laughs].
 Diablo II
 Diablo II: LoD Cinematics
The Search for Baal
 Diablo II Cinematics
The Sister's Lament
 Diablo II Commercials & Trailers
These are some of the original Diablo II trailers and commercials. Some of these have been largely forgotten.
The first Diablo II: Lord of Destruction trailer shown. It's a compilation of what would later be the intro cinematic to the expansion, but also mixed in with plenty of detailed pictures of the Worldstone, some of which are exclusive to this particular trailer.
Compilation of Diablo II cinematics in a TV spot.
The classic 2000 Christmas commercial for Diablo II. A must-see.
The 1999 E3 cinematic is much closer to the actual game. This is basically a collage of little cuts from the in-game cinematics, rearranged for dramatic effect.
This cinematic trailer was the first produced for Diablo II. The events presented in it are non-canonical; it was just a promotional video produced before the plot for Diablo II had been hammered out.
It could also be just some random church on fire, as this was so early in development, it's likely the entire story line was not ironed out by then. It's interesting to note that much of this 3D rendered material did not make it into any of the games.
 Diablo I
As Diablo I came out in a time before video games were widely advertised, there's no Diablo I commercials, but there are deleted scenes that were made, but never added to the game!
 Diablo: Hellfire Intro
|Diablo: Hellfire Intro|
 Diablo I Cinematics
|Diablo I Intro Cinematic||Lazarus|
After this cutscene was shown, it leads to the player's confrontation with Lazarus and his succubus guards.
|Warrior Ending Cinematic
We don't know why exactly some snippets were removed, possibly to save some programming, but there used to be one ending per class, but in the final game, it's only the Warrior you can see.
|Diablo Ending Cinematic
The last cinematic of Diablo I. We see the Dark Wanderer standing We don't know why exactly some snippets were removed, possibly to save some programming, but there used to be one ending per class, but in the final game, it's only the Warrior you can see.
 Diablo I Deleted Scenes
As mentioned above, Diablo I came with deleted scenes. It's not clear why some of them were removed, but they still exists in the game files, and as such are shown here. They have never officially been released.
This Butcher introduction was removed before the game went live, and it's the scene fans are most surprised was deleted. It's a tad gruesome, yes, but there's corpses and death all over the game, so it seems unlikely to be because of censorship.
|Map of the Stars
The Map of the Stars cut-scene was specifically removed since the quest itself was considered ruining the player-driven nature of the game. You can see the original Diablo render here doing something with these stars.
|Rogue Ending Cinematic
The first of two additional ending scenes that exist for Diablo I, but was not officially part of the game.
|Sorcerer Ending Cinematic
The second of two additional ending scenes that exist for Diablo I, but was not officially part of the game.