General consensus is...
that the gameplay is terrible, and its no mystery why people think so.
The camera is garbage. It zooms in and out too much, and doesn't show you what you need to see 95% of the time. Sure it might zoom out when an enemy flies near, but what about the platforms I'm trying to jump to? I jumped off the edge of a level several times because the camera view was not wide enough to let me know where exactly I was headed.
The controls are kind of garbage too. I enjoy a good MetalSlug-esque arcade style shooter just as much as the next guy, but this one does the genre no justice. In Metal Slug you could wave shoot back and forth between up and side and get shots to fire at the inbetween angles to hit enemies. I could not do that in this game, and as a result I would get destroyed by flying enemies which stayed out of my 8 limited lines of fire, and also by the wall mounted guns which were at an angle I could not shoot to.
And speaking of enemies, most of the enemies were very poorly designed. Doubled with the fact that you can only fire in the 8 set directions, the fact that they could freely pass through walls was ridiculously overpowering. While neither the enemies nor the player could shoot through the walls, when the enemies passed through the walls and fired off some quick shots at an angle I couldn't counter-fire at, I lost a considerable amount of health with no chance of defense at all. I'll also mention again that the wall mounted turrets were incredibly broken; they did an overwhelming amount of damage and most sat at angles where I could not shoot them without taking several shots first.
As far as graphics go, they were pretty phenomenal, despite watching them zoom in and out like mad. This game is a lot like Counter-Strike:Source in a way, being that it made great strides in graphics but generally just released a lousy game.
I would suggest taking some time to play some Metal Slug and really study what makes it's gameplay as good as it is (or even Alien Hominid here on Newgrounds, which is the epitome of flash game success off of NG). It's a balanced game, free from distractions like crazy camera controls or leaves blowing around everywhere. I'm sure if you take in what makes those games as good as they are, you can incorporate some of those points into this game here, and really make it something worth playing.