Halo, Gears of War, GFWL, any title that was released on 360 before PC for no reason.
Its no secret that MS would rather you buy games for xbox than for PC.
Then there was Alan Wake, which in 2005 was the first PC game that was demoed to run on a quad core processor, and its looks at the time were revolutionary. Then Remedy signed with MS, the Xbox port had to come out first, and MS made them delay Alan Wake till 2012 for the PC. By which time it looked decidedly average at best.
MS bought Lionhead Studios, and Fable II for the PC was cancelled and became an Xbox exclusive.
Mechwarrior games weren't really suited for a console controller, so MS shutdown FASA studios, ending the popular and successful Mechwarrior series.
Flight sims and RTS games aren't popular on consoles so MS also shutdown ACES and Ensemble Studios. Microsoft beats the competition in combat flight sims, and then just stops making them. They basically killed an entire genre, because the Xbox can't play it.
They bought all these PC gaming studios, and then converted them to Xbox only studios, or just shut them down.
Then there were games that used Microsoft Gaming Zone. MS shut that down. So unless the publisher is still around to switch it to another online system you're out of luck, since MS shut it down. Don't ever rely on MS for PC games, or online play.
And those are just the big names that I liked. Who knows how many lesser games never made it to the PC or were delayed thanks to MS. MS gets to see the PC games in development before we do. The best they try to make Xbox exclusives.