Lara Croft and the Guardian of Light

Vitally, these co-operative abilities don't just find their application in clearly-signposted situations. They're part of the whole fabric of the game. You develop a kind of symbiosis; rather than just standing on different switches in unimaginative puzzles, as it so often the case in co-op, you'll be spontaneously saving each other from a fall with a quick grapple, or protecting each other back-to-back against waves of tomb-dwelling undead.

Some things are a little easier with Lara, some with Totec, which lends the game near-perfect balance. It never feels like one of you is left to do all the work. Totec isn't simply the support player setting up successes for Lara, and refreshingly, the female character doesn't have to stay two steps behind a more combat-capable male. The rush to grab gems or kill enemies first for more points introduces a gentle element of competition, but ultimately you depend upon each other to succeed.

This is because every level in Guardian of Light has been built twice - once for one player, and once for two. Playing in co-op is not just a matter of squishing more enemies, or standing on two switches instead of one - the levels and puzzles are significantly different, and satisfyingly clever. Entire set-pieces play out differently, meaning that the game is still a surprise in multiplayer even if you've already conquered the levels solo. (Online co-op won't be activated until 28th September, when the game comes out on PSN and PC, but local multiplayer is seamless.)

In single-player, weights and rolling balls will often take the place of your partner, but it doesn't feel pared-down. There's almost never a moment in single-player where you're left struggling on your own with something that is obviously a two-person puzzle. Indeed, it's hard to imagine how the levels will be rebalanced for two until you play them through with a friend, and suddenly wonder how they ever worked in single-player . What Guardian of Light achieves, impressively, is a campaign that feels purpose-built and perfectly balanced whether you're playing on your own or with a friend.

This inspired duality makes Guardian of Light one of the best-value games on Xbox Live Arcade, PSN and Steam. Even after you've finished the campaign, it lives on as a score-attack game. Speed-runs are rewarded with extra relics and artefacts, and mini-challenges push you to get the most out of each level, teasing you with tricky tasks like rolling a ball through a maze in less than 30 seconds, solving a puzzle on the first attempt or jumping between stepping-stones without touching the floor.

The only thing that's lacking is a half-decent story. Guardian of Light's is barely even relevant to the action and what few cut-scenes there are only serve to accentuate its shallowness, but it does make up for these shortcomings with excellent set-pieces. There are heart-racing moments as good as anything Tomb Raider has ever produced in Guardian of Light, and they're even better when shared with a friend.

Guardian of Light would almost be worth a full price for the co-operative campaign alone. At 1200 Microsoft points - around £10, €15 or $15 - it's an instant buy. There are few download games that offer this kind of value for money, and few that are as clever or effortlessly exciting. Lara Croft and the Guardian of Light might be a move away from the Tomb Raider name, but it's a tremendous homage to its spirit.