It will be interesting to see how this pans out in 1 or 2 years. Unless MS has some big exclusives coming I simply can't see how the hardcore gamers are not going to a greener (or should I say bluer?) PS3 land.
They lost Bungie, Bizarre, Rare is now nothing but a casual studio, Lionhead may or may not be doing gamer stuff, Gears of War is supposed (iirc) to be done with the 3rd one, and Forza while being a good racing series is hardly a system seller. The Halo franchise is now in the hands of a new team who has everything to prove, even though they have big names in their ranks.
Seriously though, what the hell are they going to release after Gears 3 next year? Forza 4 is the only game from an existing IP that MS could have in store for Q3/4 2011, no Halo, no Gears, no Fable, no PGR. Unless they have a new huge IP in store (and with their current management it's highly doubtful they'd go and launch a new IP this late in this generation), MS has basically no big releases after Gears 3.