Short and easy, but it was amusing
Cool metroid-style game, but:
* It was maybe it was too easy, specially the bosses.
* It was a bit short (the level length was ok, but maybe there were too few levels).
* Upgrades ended too early; the big ones were too cheap.
Maybe it would be better to increase the difficulty more on last levels; put harder enemies that require more powerful guns that kill more and make huger explosions, more upgrades (maybe unlockable?), harder bosses that do more things than just jumping and shooting.
And now, some tips for gamers:
* Get the laser ASAP. It rocks and isn't too expensive. Also get all the life upgrades. The books help too. Guns with more damage seem to be better than fast ones.
* Spikes don't hurt much (only 1 hit point), so if you must run away don't hesitate to jump on them (but try to avoid them).
* Water slows you down a lot, so if you need to run, jump.
* Still robots are invulnerable (I think) unless they're shooting. So stand near them a few steps, wait for them to open, shoot quickly so he only shoots once, and jump the fire ball.
* The end boss could be killed without losing a single life point (well, I couldn't, but it could be done). It just shoots 3 fire balls and jumps. Simply wait for the first one to actually touch you and then jump quickly, so that the first ball doesn't actually harm you, the 2nd one passes under you, and then jump again to avoid the 3rd one. Move to another position and repeat.