It's not often a game completely exceeds our expectations. These days games tend to arrive on such a massive wave of hype that all the mystery has been washed away before you've even taken the game out of its cellophane wrapper. There's a new distribution method in town though, with download-only titles tending to sneak out without anyone noticing. One such game is PopCap Games' Plants Vs Zombies, a title so packed full of quality and charm that we can't think of anyone who'd play it and not find themselves hopelessly addicted.

In truth the game isn't hugely original. You play yourself, an ordinary guy or girl whose house happens to be under attack from zombies. It's your everyday scenario really, and it just so happens that you've got an army of plant weapons and soldiers to help you out - hence the game's title. What we've got here is more or less a game in the tower defence mould. Your house is on the left of the play area, a grid sits in the middle on which you can plant your weapons and the zombies stagger from right to left in an attempt to munch through the flora and get to the front door.

Your goal in each level is to prevent the zombie horde from getting to the house, but it's not easy. Firstly you'll need sun, which as any good gardener knows is essential for plant growth. The sun appears as collectable tokens from a number of sources: daylight levels provide you with a small but steady stream of sun, sunflowers produce sun during day and night levels, and sun-shrooms (a kind of mushroom) produce sun during the night. Collected sun is added to your overall sun stockpile, which can then be used to plant various weaponised plants on the game grid. There's an RTS-style cool-down period for each plant type too, so you can't just build up lots of sun and then spam-plant loads of the most powerful weapon type.

Early on you're going to have to make do with the basic Pea Shooter (a kind of bog standard long-range fixed weapon), the useful Wall-nut (a living, eventually sad-faced wall) and the Cherry Bomb (a close proximity explosive that explodes more or less as it's planted), but before too long there's a whole heap of plant types on offer and a varied selection of zombies on the warpath. You'll have potato mines, snow peas (slow down enemies), chompers (zombie eating monstrosity), repeaters (dual-pea firing gun) and a whole host of fungi weapons that can only be used at night - some being completely free in terms of sun cost.

On the zombie front the basic type simply stagger across the screen, slowly munching on any plants that get in their way, occasionally made tougher by two forms of head-protection: the traffic cone and the tin bucket. Then come zombies that can hurdle obstacles, a zombie reading the paper that gets irate and charges, a bulldozing American Football player zombie, zombies hiding behind grates, Michael Jackson in Thriller rip off zombies that spawn a gang of dancers, and a load more. The key here is that you're given a preview of what to expect in each level, then given a set number of slots in which to place seeds. Certain plants are good against certain zombies, so planning ahead is vital.

As you play the opening set of levels you'll likely enjoy yourself, but barely break a sweat as you mow down the zombies with ease. Before too long, though, you'll have to carefully plan and manage the planting of sun generating plants and defences in order to gear up for the final wave of zombies, in which they come at you in force. Neighbour Crazy Dave pops up from time to time to provide you with new items and unlocks in return for some cash (collected by clicking on the coins dropped by slain zombies), and he also introduces a number of mini-game-like levels that break up the standard gameplay. In these levels you're still defending your house, but sometimes with a ten-pin bowling mechanic, occasionally planting weapons from a conveyor belt, and even the odd whack-a-zombie section.

You're always having to think and make snap decisions

We've only really scratched the surface of the items and zombies you'll come across, and even the stages you'll play on, with each having its own unique gameplay characteristics. For example, the backyard level has a swimming pool down the middle, meaning you need to lay down Lilly pads in order to plant normal weapons on top of them. The game moves at such a fast pace that you're always having to think, constantly trying to position plants in the ideal location and deal with the enemies coming at you, but the superbly simple controls and interface never let you down. Although there's a load of depth here and real difficulty later on, you'll never be able to blame the controls for your misfortune.

PopCap has developed a reputation for quirky games, both in terms of gameplay and presentation, and Plants Vs Zombies is no different. The visuals are simple, but the character in each plant and zombie design is superb, as are the animations. One of our favourites is the Wall-nut, whose face starts off quite jolly, before the smile gradually turns to a frown as zombies chomp through his skull. The soundtrack is annoyingly catchy too, so don't be surprised if you're humming it for some time to come.

With a main game mode that spans 50 levels, numerous unlockable modes that extend the lifespan significantly, stupidly addictive gameplay and fun-infused presentation you'd be a fool to pass up Plants Vs Zombies. The basic gameplay isn't exactly original, but it's been executed so well here that it absolutely needs to be in your digital download collection.