Krz, I agree completely, the game's not hard enough, I spent quite a bit of time trying to balance it, but I think it has fallen too far on the side of easy.
Coconut Mage, I'm afraid I can't think of any reason why the player won't move, might be worth trying to 1. refresh, 2. delete playerprefs in Username/AppData/Roaming/WebPlayerPrefs - find and delete the .upp file, or 3. Try the download version, see if that works. I've had it tested on a couple of machines, and there are definitely still some bugs, but I'm not sure how that one could have happened.
Tuism, Yeah, I think the levels should roll over automatically, maybe once the player picks up the last power-up (for health), it could go straight into the next level, or a timer after all of the enemies are dead. And then they can turn that off if they like, or change level whenever they like. I really wanted to make the level changing element a central mechanic, but I never really achieved that. I was move focused on polish this time round, I'm thinking of working on the game a bit more; push up the difficulty, add a proper menu, more level variety, more enemy types that have different weapon behaviors, etc. I think I've nailed down the controls and flow of the moment-to-moment gameplay, but it could be so much more!