I really have to be honest - it's just a dull game. I found it silly that you can't just click to shoot, you can't just tap U to upgrade, but the slightest tap of the space bar had you using a mine whether you wanted to or not. It made the control feel really inconsistent. There was no variety in enemies at all. However, what I found the most frustrating was the lack of an option to just start over when you got a game over - you have to refresh the page, and that's a really basic component of a game. You want to give your players the option to just try again, rather than pushing them away when they fail. On top of that, for some reason, once you get a game over, you can still use you mines.
It has a long way to go and a lot of improvements to make before you can call this a decent game. Games like this are incredibly fun when done right, and I certainly think you can fix it.
Remember, give it some variety, fix the controls, fix the game over bugs, maybe an overhaul on design, and you could really have something. Maybe even get the aid of an artist or fellow programmer in the collab section, most would be more than happy to help. Perhaps at a price, and perhaps not.
If it's your first attempt at a game, you did a great job, and just remember, all you have is room to improve yourself, and your games!