Really Addictive... and SAVE OFTEN!
Diablo is the closest I've seen to a graphical Rogue/NetHack. Ultimatelly much better than SSI's Dungeon Hack, Diablo combines Isometric 3D action with some cool effects.
Graphics (for 1996) are astounding. Spells, weapons, gold, and items are produced very well. I can't tell if any of the action was motion captured, but it looks like it. Either that or the animators study humans walking for hours. The sprites used in fighting and walking are very realistic.
The sound is great. The clash of steel against steel, the creaking of doors, the *phhhooooomp* of the arrows, and especially the creepy "Bad guy" voice. Ambient sounds make or break a game, and this one does nicely. The voice-acting suprised me. Blizzard was smart to make the people you interact with in the village staionary sprites. Syncing Graphics and voice-overs is probably one of the biggest pitfalls of games. Blizzard's use of scrolling text/voice overs give you a chance to either listen to or read conversations. No japanese dubbed actors here. :)
The gameplay is addictive. Period. I played NetHack and Rogue for hours on end just because it was different EVERY time you played. The same goes for Diablo. The game is never the same twice. The goals will be the same (find Odgen Sign, defeat King Olrec, etc.) but the actual dungeon gameplay will be different. The replay value alone is worth it.
The Control is mainly mouse based. This is great if you have the new IntelliEye mouses with no moving parts. But for those stuck with "old reliable" the controls can get frustrating. Left click to move, left-click to attack (when stationary), right-click to cast spells, and right click to use items off the main screen. So needless to say when you are in the middle of a HUGE group of skeletal warriors (as I was a few nights ago), if you twitch at the wrong time, you can kiss your armor goodbye.
A minor complaint are the dungeon walls. It's very difficult to maneuver around with the "partial" walls that allow you to see in corners. You almost ALWAYS have to play with the automap feature on, and even that becomes distracting in a melee round.
The Bottom Line
Overall, Diablo is a fun, addictive dungeon hack. If you liked Rogue or NetHack, this '90s version is right down your alley.