I really hope it will be gameplay-wise something with ME2's combat but with slightly richer RPG elements. In case of story I wish there will be epic battles across the galaxy against reapers. It would be great if we skip few years (or how much it takes from the reapers to arrive) and the game would begin just few days/weeks before the arrival of the reapers.
By the way, I don't have anything against PS3 version and I think it's good that more people get to enjoy ME universe but there's one thing I'm afraid... Since PS3 players will get some kind of brief explanation of ME1's events and get to make some key decisions there are lots of things they will never hear about. Some of these things like what you decide to do you with Rachni Queen have barely no meaning in ME2 but I think that in ME3 friendly Rachni fleet could change everything.
Anyways, since PS3 gamers don't probably get to make some of these decisions and PS3/X360/PC versions are equal story-wise, I'm afraid that some decisions from ME1 won't be implemented and therefore the gameplay experience might lack something it could have had.