The game is different to the previous Lara Croft games - it's an isometric slightly platformery/hack'n'slash/collect the treasure game. I believe there's single player but we were interested in it for the local co-op (no online co-op as far as I can tell in the PS3 version, I dunno about the Steam version). The set-up/intro sequence of the game is Lara Croft & some bad guys get to some ancient artifact in an Aztec temple, the bad guy picks it up & uses it and unleashes an ancient (evil) god and an ancient statue of the guy who defeated him initially (Totec) comes back to life. So now it's Lara Croft & Totec fighting their way out of the tomb to defeat the evil god who wants to rule the world. It's divided into levels - each one has a set of objectives, like score a certain amount, or do it in N minutes (where N is very small - the one that we spent an hour exploring & playing has a goal of 6 mins), or find all the red skulls, or blow up all the trucks, etc etc. And these give it a lot of replay value - the short time objective is utterly incompatible with the collect the set type ones, or the score high ones. You get score by collecting gems and shooting baddies & monsters - in level 3 we were setting spiders on fire with flame-throwers :D If you complete objectives you unlock items (which are there on subsequent play throughs), and you also find things like guns & power-ups in the levels.
I believe (from wikipedia) that the single player experience has Lara as the only playable character with different abilities, but in 2 player mode one of you plays Lara (me) and the other plays Totec (J). Totec starts off with spears & a shield, Lara with her pistols and you collect other fancier guns throughout the game (guns for Totec too, Lara teaches him how to use them as evidenced in a cut scene at the start of level 2). The initial weapons have unlimited ammo & both characters have limitless bombs to blow up obstacles & enemies, better weapons use varying amounts of your ammo bar (like a mana bar in a magic-based RPG) - the flamethrower eats up ammo like you wouldn't believe, it's still cool tho :D The co-op aspect is very well thought through and you use both characters together to reach areas or solve puzzles. For instance Totec can hold his shield over his head, then Lara can jump on that to reach a higher level. She can then fling her grapple line down to Totec & pull him up. Also if Lara flings her grapple line to a ring on the opposite side of a drop then Totec can use it as a tightrope. There's been multiple ways to do some of the puzzles - we did one on one play through of a level by a combination of Lara using a spear flung into the scenery as a platform to get to the top and then over a pillar to get to the switch to lower it for Totec. Then on the next play through Lara jumped on the spear & Totec used a switch to turn the pillar so she didn't have to climb over the pillar to get to her switch to lower it.
We spent about 5 hours yesterday playing it :) We'd initially thought we'd just play the demo, see what it was like, maybe buy it later. But then we got to the end of the first level (that's what the demo is) and it offered us the chance to buy the full game (or quit the demo) and we went and bought it coz we'd had such fun with it! The full game purchase is very well integrated into the demo - it asks if you want to buy it, you say "Yes" and it takes you off to the store where you pay your £9.99 and download the tiny unlock key which installs & you're sent back to the game where you can now continue your saved game. We actually decided to delete the save game & start over (partly coz we saw we'd hit some trophy conditions in that level so we might as well get them by repeating it). And then we played through to the third level, which we repeated to try & hit the score objective with at least one of us. And then I had to cook dinner else we'd be hungry & after that there were other games waiting for both of us. But we're gonna get a lot of play out of this, I think :D
So in conclusion, well worth the 10 quid & 2.5Gb download - in fact I'd say we've already had our money's worth and there's another 11 levels left plus replay potential in the ones we've got (like I'd quite like an auto-shotty for Lara, so we need to re-do level 2 skewing the score collection to my character this time so I get that unlock). If you're looking for a two-player co-op game with some of the feel of the Baldur's Gate: Dark Alliance game on the PS2 then this is definitely worth a look (and in fact it has better use of the co-op aspect). And it's got proper Lara Croft style & witticisms, it's gotta be good (I love the things she says).
(It might also be a good singleplayer game, but I've not tried that so can't comment on it - the co-op is drop in/drop out too, I am lead to believe by wikipedia, but I'm not sure how that works either.)