For a game made in 48 hours, this is actually pretty fun!
It is simple, keeping with the minimalist style of gameplay I see with a lot of pixel games, yet it keeps ones attention with its addicting, easy-to-master sense of gameplay. The evolution branching was great, as it gave almost a story to the game, and gave the player a sense of power over directing where his character was to go, as it should. Should he be a slow moving, fast firing turret-like little guy? Or maybe a quick, lightning-bulleted sniper? You may only be controlling a few pixels, but you can use your imagination to shape the character into anything you want...even though he never really changes in physical appearance!
Another thing that made me weep tears of joy was the fact that you are not penalized for failing a level. Not only would it change the way the game worked (would this be a detrimental factor or not?), but as a plus, it does give you leeway to "level grind" in a sense and rack up points at your own pace, creating a relaxing, almost stress-free state of mind while playing this mid-paced game, knowing that there was no pressure to level up a certain stat by a certain level.
But let's not forget that, sure, there's always room for improvement.
The arrow key controls are alright, but there was a problem I found myself having that made moving smoothly a bit difficult: using all the arrow keys to direct my little character in that specific direction. I would have found it easier if the controls had been more along the lines of, for example, using the up arrow to move forward and the left and right arrows to steer, as apposed to using up to move up, left to move left, etc. Of course, this is because I am not familiar with this type of control system, and others may find it easier to use. In fact, once my fingers stopped fumbling around and figured out how to work right across the keys, it was only a minor damper on the enjoyment.
Another thing would be that the levels are lacking a sense of...variety. Yes, being made in two days does add a significant amount a pressure to even /finish/ the game, but I think that maybe having something like different enemies as the levels progressed, or maybe enemies evolving into different shapes as you evolved attack methods, would break the monotony and make it feel less like one was slogging through an endless loop of the same level. Maybe there would be other things to upgrade, like a spread shot instead of the single stream of fire? I don't know. The enemies appear to move faster as the levels go on (maybe not...I can't be quite sure), but that was about it.
So, all things considered, I think the three-and-a-half star rating was pretty fair. The game was entertaining and fairly easy to play, though a bit monotonous and the controls were a bit odd. I hope this is helpful!