An interesting take on the theme; I've played another game that had the same concept (The End Is The Beginning), but the problem I have with this approach is that the way a player approaches the levels when 'rewinding' is not the same as how a player plays a level from the 'normal' way (i.e. level 1 forward), as demonstrated when I got to the end and then had to go back through normally (some parts you just fall down rather than have to jump precisely). I dont know if that's really anything you can change or fix tbh, just a comment on how it isnt exactly playing as if you were rewinding a game :P (also it would be a pretty weird game design if the final level i.e. lvl10 was one of the easiest in the game :P ). I did quite like the effect of the bullets rewinding though.
It is interesting how the brain gets in a flow of treating left as right and vice versa, but as soon as you stop for a moment it gets confused on the next jump haha (like i would complete 10 jumps with ease; then have a break on a platform, and the next jump i would be confused hahaha, silly brain).
Only real comments I would say in terms of what to improve are:
>the game would be helped with audio (i didn't hear any, was there any?) to set a mood
>You should let the player know what button is shoot rather than telling them it isn't left mouse click (why wasn't it left mouse click btw? I dont think W is the opposite of left mouse click :P I expected shoot to be S when going the 'normal' way )
>The post processing effects were cool initially, but later on got a bit strainy on the eyes I felt; nothing too major, but I think they could be toned down a bit.
A decent platformer overall though :)