This is the kind of game that I pick up, play for 5-10 minutes, then I realize there's nothing else to it beyond a very simple mechanic and I lose interest in it because I mastered it but have no further reward that makes me want to keep playing.

-Graphics and sound are mediocre.
-No tutorial but the learning curve is so easy it's not a big problem.
-The randomness of some of the effects doesn't feel challenging, it feels downright annoying, that's a problem. There wasn't a predictable pattern so I felt helpless once the effects started.
-The victory message informing me that my plants survived seems completely disconnected from what I'm doing. What plants?
-Difficulty levels don't make sense. Low? You mean Easy? And it's not easy, it's pretty hard sometimes. Sometimes hard is easy. What's going on?

When I play games, I like to get to the options menu first thing. This game, I couldn't figure out how to change anything, so ordinarily I'd look for instructions. No dice. That's terrible. I grew to hate having to click to move pretty much immediately, which means the controls need a lot of work.

-Learning curve is fine.
-Graphics need to look less like the aftermath of a nuclear winter directed by JJ Abrams, but are otherwise great. Just tone down the bloom or make it configurable.
-Fix the problem where you can't leave the levels area without restarting the game.
-Make an optional menu for the settings so you don't have to use an awkward in-game one. The novelty wears off fast even when done right.
-Why do bullet-shooting guns have charges? Make the guns look different if you're doing energy bullets.