The core gameplay just isn't that fun, and with much better shooters on the PSN, you shouldn't get this game.
The gameplay has an interesting twist. You are put into cubes with attached blocks making up a level. If you kill the enemies fast enough in one block, you go to the next harder block. The point is to go through every path it seems, doing levels as fast as you can. Every few blocks, there is a boss battle, generally in the middle and then again at the end. Some of these are pretty easy, some are friggin hard. It sounds cool, but it just gets old really fast. I couldn't keep playing this game after a couple of hours.
The graphics are really good for sure. Everything looks cool even though each level is made up pretty much of one basic color. The sounds alright, but nothing special.
Overall, I don't have much to say about this game other than the fact that it just isn't fun. This is really the only game off of the PSN I wish I hadn't bought.
(On a side not, Sony should set up a buy back thing where they buy back the on-line games you purchased if you want them to and they give you some dollars to use again on the on-line store. I'm not asking for much! :>)