Well done, but not interesting
This is clearly a well-done game, and it's obvious that a lot of work went into it. However, there are a lot of little things about it that bug me, and it doesn't really bring anything new to the table for its genre. In fact, it's sort of bland for a side-scrolling wasd+mouse shooter. It just doesn't have the depth or atmosphere of classics like Abuse, nor the fast paced insanity of similar flash games like the Thing Thing series, nor the challenge and variety of the prototypical Mega Man series.
The specific things that bugged me follow. It is entirely possible to evade enemy bullets, in many cases indefinitely, by running in the other direction. Most of the enemies lacked a 360 degree firing arc, too. These facts combined mean that the vast majority of the enemies posed almost no threat to the player. In fact, I don't think I took any significant damage until the spheroid boss, which essentially covered the entire screen with bullets. This brings me to my next point, the fact that there is no continue option. I got all the way through a slew of tame robots to lose to this boss, the first point in the game that wasn't forgiving in the extreme, and I had to start over.
My last gripe is the weapons. Most of the upgraded weapons seemed like mere augmented versions of the default gun, without any quirks or specialties. The ones that did act differently, the C4 and the flamethrower, were pretty much useless.
It's apparent that a lot of time & effort went into this; it's relatively polished, it's bug-free, and its presentation is pleasant. I'm sure that it's really hard to make a game like this. However, I would have liked to have seen more of that time & effort go into gameplay, variety, and balance.