Overall it was a good game. Like others have said, it is rather short, but it was fun for the time. Once everything is upgraded, it is also very easy, especially at the beginning, harming its replay value. I also found that Snake might have been a bit overpowered. That humble cardboard box, fully upgraded and with a very fast recharge time, saved me more than a few times with its invisibility and invincibility. I found the other characters' abilities to lacking, except for Isaac's force field that can push everything away.
It is still a good game, and if the game were longer, maybe had a harder mode or harder area, and the character abilities were tweaked a bit, it could be a great game.