I'll be straight with you, I didn't find this game overly enjoyable, nor interesting to look at or ground-breaking in any way, but it did serve it's purpose. It gave me something to do while waiting for the movie to start.
The graphics aren't bad, it's not that, it just all seems like it was made in 2008 or 2009. These kind of graphics might appeal to some, but not to me. There is no underlying storyline to the game, which really isn't necessary for a timewaster.
A timewaster will, however, never score high in my book, because they aren't entertaining, they just somewhat suck you in.
The upgrades give you some sort of customization, which is nice, it adds something to the game, but I can't say it changed a lot, at least I didn't notice it. The difficulty curve is also a tad steep, first level beaing incredibly easy, but on the fourth or so, you're getting swarmed, and unlesss you choose the right upgrades, it's hard getting out of it alive.