The idea behind this is genius. :D I would have never thought of something like this just from the keyword "roll". However, I could not make it past the second level. I don't know if I did something wrong.
Also, I think the controls could be improved by making it possible to rotate the sniper's aim just by simply right clicking. That would be more conventient in my opinion, but it's not that big of a deal either.
Anyway, if this is really your first game ever, then I'm impressed. :D The idea is great and I think you should further build on this basis. :)