It's a bit clumsy to play alone, but totally doable at this difficulty. I imagine the Sprout player will be a little bit bored (at least in the beginning) because there's not so much to do over there. Maybe make the vegs fight each other (Dem Yukon Golds refuse to be placed too close to the Carrots!)/rot if not harvested quick enough, or would need some other ways to care (fertilizers?). Then again, when playing local co-op, the spare time may be used to jeer on the Tinker player. On the Tinker side, I can never quite accurately place the crops. It might be a mistake on my part but it does feel like there are spots I can't drop them on (outside the no-plant zone, of course).
Overall, a nice rendition of Plants vs. Zombies. I sure do miss that game, there's nothing quite like it as commercial tower defense games tend to lean towards 'serious themes' instead of zaniness...