It's a simple level but it's not bad. I think if you were able to rip the DS versions of the plants vs zombies sprites, the zombies would look a bit better with the style of the Mario graphics.
The only thing I would consider a negative is the boss fight. None of the spawning items are telegraphed that well, and the rinkas are *just* a bit too much. Compared to the rest of the level, the whole sequence is quite a difficulty spike.
I also don't understand the sudden focus on spinjumping about halfway through, especially when the first spinjump is across a very large gap. I think if you foreshadowed the spinjumping a bit earlier, it would mesh better.