I finished the adventure mode last weekend with no problems (hardly surprising after having completed it several times on the iPhone). My reward for this achievement was unlocking a whole host of new goodies including mini-games, puzzle mode, survival mode and the Zen garden. Hurrah!
I've just dabbled with the puzzle mode - the vase smashing is good fun and requires a bit of thought, and the I, Zombie mode turns the whole concept on its head with sending zombies to chomp flowers. The survival mode is a good challenge, and I managed to last seven waves on the daylight hard setting last night. I have a plan for the hard night time pond level involving building a row of cattails all the way across the screen to shoot the balloon zombies with star fruits and gloom shrooms along the sides for heavy fire power.
The Zen garden is a wonderful change of pace, and is really just an excuse to potter around, watering and feeding plants and listening to relaxing music. It's also a nice money spinner to earn cash to spend in Crazy Dave's shop.
All I can say is that it's a good job that Popcap games don't deal crack ... :-)