I'm also looking at creeper world
I tried the demo and it was fun. Although a bit too easy. But I guess the missions will get harder towards the end. I'm sure it's a good game to play on days when you're too tired to play complex and challenging games.
I have that game, it gets a heck of alot more complicated as time goes on. Doesnt take long to do that either; that's not like really late game where it hits that point. It introduces all of the different gizmos at a pretty quick pace and goes from there. You end up having this sprawling, tangled mass of a base with generators and conduits and other whatsits going every direction all over the place, and then all sorts of towers (and often more tangled mess out by those), which often need to actually be moved. Like how Terran structures in Starcraft can move, they can be shifted around almost exactly like that. There's never enough space, your power is limited, the overall structure of your base + the surrounding landscape gets complicated, and there's quite alot of different thingamajigs to build, and making the wrong choices will just get you wrecked.
There's also a sort of "aggressive" style to the game. Other tower defense games, you have your specific area, you build in there, and the enemy comes to you. In this, there's usually some "core" or something that you need to reach, which means you need to expand constantly INTO the Creep-filled territory. I like that part alot; the game never really feels like there's anything in the way of WAITING, which is a problem this genre often has.
The demo areas are stupidly easy and really dont convey much of it... I've never liked demos, for pretty much exactly that reason. Usually dont bother with them.
I personally think the game is pretty darn great myself. Tower defense as a whole can make for alot of strategic depth and they can get hard as nails, but they're usually a little too formulaic, sticking to certain trends a bit too much. This one really doesnt.