Meh
The upgrade system was kind of cool, but...
The fact that any upgrades you have are decreased by one at every level-up is kind of terrible. As well, the fact that you can't shoot in both directions at once increases the difficulty far too much if you're introducing swarms of enemies from both ends. As long as you're on a Touch Of Death type system, this style is too much.
The game is, in conclusion, very very difficult. If you like it that way, go for it. If not...