This is not normally the sort of thing I would install on my computer, but after trying the free online demo version on Popcap's website, I had to buy this and it really is such good fun that it has led to sleep deprivation!
You need to protect your house by dropping plants in front of it to destroy the zombies, which march relentlessly towards your house with the aim of getting in to eat your brains. There are 49 varieties of plants, including pea-shooters, doom-shrooms, hypno-shrooms and chompers. As you progress through the levels, you unlock more and more plants and zombies, and also some mini games and a zen garden. Finishing the Adventure mode unlocks further mini games, puzzles and play modes.
You also need to collect coins as you go along, which you get to spend in Crazy Dave's shop on upgrades / new plants etc. The whole game is really compelling and although the graphics are simple and the music somewhat repetitive (the soundtrack, although brief, is great and you will find yourself humming it from time to time!), it doesn't grate at all, there is enough variety to keep you playing. Some of the mini games and puzzles are themselves very addictive. Also, because the game is undemanding in terms of specifications, you can play it on pretty much anything - I have installed it on my netbook and it works brilliantly - perfect entertainment when you're travelling.
I bought this game from Popcap's website before it was released on disk. The disk is cheaper far cheaper than the download, so this represents extremely good value.