It's not really. First of all, Plants and Zombies had a much more fine tuned balance. I played Orcs must Die! demo and went through all the levels it has, then replayed them. I was never, ever even close to dying or letting a single orc through. I couldn't try the hardest mode because it doesn't seem to unlock in this demo.
The game is fun. Not as rewarding as PvZ, in my opinion the gameplay is not even close to as refined as PvZ.
Still. I didn't find bugs, the game ran very nicely on my setup and I had some fun. That's $15 worth, I'd say.