As good as the 1st game, with a few improvements and a few points where it's worse. Doesn't matter, More Orcs Must Die!
Still, there are amazing improvements: one more character, better upgrades structure, more weapons and traps and guardians and, the best, the co-op mode.
Co-op was exactly the major flaw of the first "Orcs Must Die", lots of people started playing "Dungeon Defenders" instead just to play co-op. Still, "Orcs Must Die" single-player manages to be (against all odds) yet more fun than "Dungeon Defenders" multiplayer, and now that we have co-op in "Orcs Must Die 2", well, there are not many reasons to go back to "Dungeon Defenders".
In the end, I think "Orcs Must Die 2" is as good as the first one (meaning: it's amazing!) and also very cheap. Insanely recommended.