No, it's fine. Not great. Good/fine. It's certainly not the best tower defense game, but what it really does well is encapsulate the 'tower defense' game into a quick, almost actiony experience, perfect for a mobile device.
To put it in perspective, you can beat most missions in under 90 seconds or so. Missions aren't long and drawn out like they are in most TD games, from PJ Monsters to Defense Grid to Kingdom Rush. As such, even losing doesn't sting -- you'll never feel like you wish you could turn back time 3 rounds.
In it's place is tappity-tappity tap -- you're using that minute or two to throw down defenses and resource generators, upgrade, and fire off various 'special attacks'.
There are also some 'endless' score attack missions that are pretty damn challenging.
While it certainly isn't the best TD game I've ever played, it's really good at being a solid 'pick up and play' TD game due to mission length.
In feel, it's probably most like something like Savage Moon --- robotic bug like enemies. The game may not be something special, but I've played dozens of far worse TD games [and many better, to be fair, since I don't mind long drawn out ones].
It's also an easy platinum.
