Just watched a piece of the gameplay video (did not play the game itself yet): what are these odd "click" sounds during the whole game - is he reloading the weapon every 1-2 seconds? Together with "no background music" and the "ohh/hhmm/huh" sounds on each jump it sounds rather ... not so attracting.
What I mean is: add some ambience music track ... and avoid playing so remarkable sounds in a repetitive way.
Just imagine you have a match 3 game ... and the only effects you have are a remarkable "click" sound on EACH click you make on the tiles. And on each match you make, you add a "explosion sound" ... it would sound not effective, but "annoying".
Maybe others see it different - but I wanted to mention that.
Graphically wise it looks nice (albeit the levels look a bit too ... dunno ... "clean" to me ... they look too polished without "melting" together). Maybe add a little debris here, a bit random decoration there (in the background) - so it just does not look like "background + level tiles". Level tiles should not look like a "new layer", they should look like they come out of the background elements. The first level ("rocks") tries it a bit - but the background looks too much like "tapetery" (maybe some "holes" or "deep cracks" would help to avoid this "repeating tiles pattern"-look).
The "grass" does not have any shadow and looks "flat" - like a shadeless paint of something. Palm trees throw a shadow - am not sure if the shadow fits to the shadow the "deeper" platforms throw (on which the trees grow ...so they are more near to the background rock and should have a less "offset" shadow as they reach background earlier).
The second one ("jungle") has the issue of very... uhm... big palm trees? I mean - how big is Tommy gunn then?. The "level elements" there look artificial because of it - they fly through the air without being "grounded" somehow -- you might have played with some kind of "bamboo fence" in the background or - some "construction aid" which holds all elements in the air. Assume other games might have some lianes spanning over the screen randomly. Sorry, cannot come up with better ideas now.
The benefit of the current "distinctive" approach is a good visibility of the characters - things look "clear" and you know what is foreground and background.
The other levels ("metro" and "boss") suit more visually.
Main character has some "look around head movement" (video at around 1:40)... the figure runs and jumps rather quick, but the head is moving slowly. I doubt soldiers would move their head so slowly "looking for enemies". Just do this movement on your own - how would you look for enemies in a "cool and experienced soldier way" (not how it is done in reality - but how do "80s action movies" do it - as this suits to your game). Also there is this odd "head position change" between running (face visible) and jumping (head shown from side) - without any "morph" from A to B (maybe there could be some "inbetween frame" be added?).
Maybe the "clean" look is based on the drawing style itself - like a "toon render" without any "grain". So do see my post with some more or less fine grain of salt - and see it as a personal feedback, not a "general advice".
What I _really_ liked was the font choice in title and highscore screen... this "bold" font face cries "army", "soldier", "bullets". Well chosen.
What I _really_ miss is "dirt" ... action is dirty, explosions add debris, throw around stones, dirt, ... so dunno, maybe have some "grain". Less "almost shiny" polished graphics. This is of course not the task of the developer but the gfx artist in your (inofficial?) "team"

Remember: do not get me wrong - the entry looks good, to use some "external" graphician pays out for you Xerra... your games become to look less "coder graphics" and more appealing. Each done game will improve your skills - and I am sure there will be a game which makes even me - the nitpicking Derron - only being able to write 5-6 phrases of critics for this game then

bye
Ron