The transition from PC to iPhone meant the removal of the Zen Garden and some of the mini-games, I know. But having played it on both platforms, I can't recommend the iPhone version of the game enough. The touch screen mechanics of the iPhone seem to have been made just for this game; it's completely intuitive. Tap a plant, tap a spot to plant it. Collecting sun is simple and fast. There's certainly nothing wrong with the mouse and keyboard way of playing Plants vs. Zombies, but the iPhone version feels so right that it'll be hard for me to go back to playing this on the PC at this point.
You might miss some of the removed features, sure, but for, what? $2.99? And only about 35MB of space required? If you have an iPhone or iPod Touch and you don't have Plants vs Zombies on it right now, you're doing it wrong. Get it!