Orcs Must Die 1 & 2 are some of my favorite games ever. I will say, however, that OMD2 is much more oriented towards multiplayer. If I had not played every level with a friend of mine (repeatedly), I wouldn't have enjoyed it as much as OMD1, because the maps are almost exclusively split to the point where it is significantly easier for each of you to guard a different route. I'm not as good at that single player, so it would have probably frustrated me.
If you can get a friend to join you though, it is perhaps one of the most fun games I have ever played, bar none. And they just recently added Steam Workshop to it as well, so now there is player made shit to mess around with as well.
For the money, if you don't buy it, you're supporting terrorism.