It seems pretty cool! There are multiple problems.
First of all, you can't see the exact cooldown of your plants. They are simply greyed out, but in the original PvZ, you can always measure how long it will take before they recharge again because of the way the seed slots were designed.
Second of all, The spirit cannon is poorly explained and I needed to read the information on the game page just to understand what it was talking about. At first, I thought it was just a bugged plant that you forgot to program, but when I read the text on the page about it, I realized it was a game mechanic.
Speaking of game mechanics, there is no shovel. This makes it very hard to recover from bad placements and quick reflex placements of Wall-nuts and such. I feel that it would be much more imperative to get a shovel in place of the gimmicky spirit cannon that's somewhat difficult for new players to deal with in the first place. The spirit cannon should wait for another world, but this is such a small game that a replacement of objects couldn't be done. The shovel being unlocked by default would be the best option.
Also, the first-person section feels funky to play with. Aside from the high sensitivity, it's also kind of hard to quantify what you are colliding with and what you will collide with. Jumping on bubbles felt weird because I could distinctly remember their sprites disappearing from my feet and I thought I had popped the bubble. The bubbles seem to just disappear out of nowhere despite that, and I'm not even sure if they're still there anymore. Do they go away after time? The game doesn't go into depth on many of it's core mechanics...
Also, I consider it a great weakness for the Whimsy to have collisions, likewise for them to be moved around by the player. The Whimsy commonly gets stuck on enemies and even on the player's own head.
The game was very fun, probably because Tower Defense and First-Person Shooters are my favorite genres, but this works, but it needs more work...