Length and replayability is something I look for in a game, and Diablo 3 lacks neither. As a completionist that explores every corner of a map and repeats areas for as many achievements as possible, Act 1 of Blizzard Entertainment's Diablo 3 took me over 20 hours to complete. If all 4 acts take me as long, I'm looking at roughly 80 hours per class to finish the game (5 classes puts me at a total of 400 hours), though a person going from point A to point B could easily finish 6 to 10 hours, then take on nightmare, hell, inferno difficulty levels. Once reaching level 10 on a chartecter, they could also start hardcore mode, where dying is permanent. If you think about replay for loot, upcoming pvp, and achievement grinding, that's a lot of time.
While I've heard complaints in general chat about D3's graphics, I'm enjoying them. There are stylized, inky textures and scenery strewn with corpses. It's very atmospheric, whether in a pool of light with spiders of all sizes creeping around you in the dark or exploring a desert that kicks up sand. The two cinematics I've seen so far are amazingly detailed, to the point I stopped to wonder and be sure the rendered characters were not real actors. I must admit, however, graphics are not my main concern in a game; I still play Ms Pacman with as much enjoyment as I did growing up.
How a game plays is more important to me, and vaulting on my Demon Hunter over zombies while shooting midair is a seamless enjoyment. Creatures burst from walls and out of the ground, some crawl out of molten vents and remain on fire; they explode and splatter, sometimes spilling guts that include more monsters to kill. They hiss and die with gurgles. The appearance of carnage matches the speed of the controls. Walking around, you can expect to be jumped by a horde of evil beings at any moment, and maneuver around easily as you put them down in droves.
The controls are basic with attacks bound to the mouse as well as numbers 1-4 on your keyboard. Normally, a categorized type of attack is lock to a specific key, but in elective mode (I recommend this), you can bind any attack to any button, giving you the freedom of deciding how you want to play your class. With each level gained, you unlock more and more abilities, runestones to change those abilities, and passive abilities, and you can also equip and train a follower (templar, enchantress, scoundrel) in a similar, minimized manner. I find myself debating what abilities to choose and their bonuses every time I level, because every choice literally alters the tactics for taking out monsters, and the higher level you are, the more choices you have.
If I have any complaints, it's been the occasional lag that has resulted in death. I have an older PC and multiplayer is so choppy I prefer to solo. I can't imagine attempting hardcore either, until the servers are a bit more stable. Dying because of a mistake is a lot easier to deal with than dying because the game froze while besieged by hell's minions.
Also, my monitor is small. It's 20" and even if I wear my glasses, I have to squint to read chat. It gave me a headache last night, and I have yet to find an option to increase its size (that's what she said). It seems a minor complaint, but I find it almost inexcusable to not have UI preferences as varied as talent options at this stage of online gaming, especially a dungeon crawler centered around player interaction that makes chat necessary.