I liked it. Its always the little things that make a game shine. The little puff of particles when you land, the sound effects were nicely timed for the jump, landing and killing blocks. I liked the jumping motion, it felt smooth to me. Nice scaling of mechanics as the levels progressed. nice background music, and thank you for providing controls to turn it down.
You may be developing on a 22" but I am playing this on a laptop and I cannot see the entire game area I had to scroll up and down at times to see my character.
The white for the main character is not clear enough, its was difficult at times to see where I was. Either make the grey background darker or make the main character brighter.
It was a bit of a supermeat boy story line rip off :D right down to the mustache on the bag guy :p. Great work for a short project. Its a million times better than most of the construct/unity engine shite that's posted on the site daily.
For a first game its very good. Its a lot better than my first platformers. You have a lot of promise as a developer. Replace all of your sprites with some nice art and animations it will be 4.5/5 from me. To get the 5/5 you would have to come up a new unique game mechanic or challenge. There is simply too many platformers around these days, to get noticed you have to be a little different. But as you said, its your first game, these things will come in time. Great first game effort.
But hey, what do I know :/