Good game
The game looks good, missiles have glow, there is debris, explosions and the robots look cool.
When it comes to gameplay it is pretty straight forward and gets repetitive. The missions are basically the same thing, you go from room to room and eliminate the threats encountered. Gather key, go to the next room. Sometimes there are bosses, but they don't add much variety.
The difficulty is pretty linear, and ok as it is.
There are some different weapons, which is nice, tho there could be more. The other upgrades don't contribute to variety, you just need to get them to do well.
The achievements gave you upgrades, this I think is awesome. It's fun to get random upgrades. :P You could only get them at the end of the level tho, so it's no use until the next level. Also the achievements were based on statistics, so it doesn't change the repetitiveness much.
Also there were a few bugs, like sometimes the first store would stop working, and once I tried to buy a thing that increases your HP, and it took my UP, but I didn't get the item. Not sure what happened there.
The music was good, I didn't think it got repetitive, and it had a kind of a futuristic/industrial feel.
People are saying they want a story, but I skip the story 90% of the time in games like these. Personally I think a story might just have been annoying.
All in all it remains rather bland, and has a lot to improve on contentwise. Technically I think it is a good game, so you should keep it up!