Challenging and fun game! It took me a while to understand in what direction the h atoms shoot. You could indicate it with an arrow with different colours for each mousebutton. - I just read the other comments and apparantly there are shields, sorry I'm really bad at reading instructions - Other than that it handled well and the game play was fun. I played it a couple of times and started to only bumped into other H2Os on the last tries and got to vaporize much faster. No shots (or shield) needed. I think I'm getting it, but I still don't have a clue what the power ups do, beside the energy one. I think the game runs fast enough without needing them and it definitily has replay value with the given time score. The graphics are very simple, but effective and fitting. The music is not really my thing, but it doesn't bother me either. Loved the cutesy faces of the water molecules. Great game, keep on bumping!
There is no button or key that I know of to get back into the main menu.
PS: If I'm a water molecule, why is everything around me wobbely like I'm inside a much finer liquid :P ?