Shallow but addicting.
First thing, this game is addicting.
Another level deeper down the dungeon, overpowering your enemies, finding loot, a skill upgrade, you know the drill. It's addicting.
Second, it's shallow.
It doesn't build a believable world you'd like to lose yourself into or care about. The world is just a small town and many many randomized levels you teleport to and from. You don't have the feeling of scale you had in... say, Dungeon Siege. The vast span of the land. The thickness of forests, the huge chasm when you crossed bridges, they were breathtaking. The story is generic and bland, easy-forgettable. Even more so than that in Dungeon Siege. And that's a bad thing.
There's also too much freaking loot, to the point where you don't care anymore. That happened in Dungeon Siege too, but here it's worse. I want to care for the stuff I'm wearing and be glad for the stuff I find. There's so many enchanted, rare and unique items, it doesn't mean anything anymore.
The art direction is amateurish. I don't have anything against colored cartoonish graphics, when done right. Here, the colors don't harmonize well, they're just... intense. Same with all game graphics. They're ok, they're there, they're done, but the style is not polished enough. Blizzard has a better art team for D3, obviously.
The game does everything to make your life easy. That is good but also bad. The fights are easy. The pet can carry as much as you do, run into town to sell its loot, cast magic and wear rings and amulets; it has the same level as you have and takes care of itself very well, there's no danger of losing it, meaning you don't get to care about it.
Technically, the game runs fine, even on old machines. All the interface elements meant to make your life easy are there. The initial load is way too long, and there's also longer-that-necessary load times in the game.
All-in-all, a diablo clone done decently, but one that is easy to forget.