There's nothing a controller can do, that a simple mouse and keyboard can't do better.
Now you'll say you are kick-butt with a controller and terrible with a PC. But that's because of the 10000 hours you've spent on a console.
The user-bandwidth available thru a mouse and keyboard is like an order of magnitude higher than a controller with bang-bang 'joysticks'. There's a reason online gaming separates PC clients from console clients. Just watch the console users trudging around a virtual landscape like a tank, turning jerkily and aiming erratically. Then watch a mouse virtuoso leap about like a ninja and literally run circles around the console folks.
Analog control for a flight sim or racing game. Mouse and keyboard is absolute shit for those.
Platformers also really aren't great.
That's a bit of a blanket statement, no?
The PC controller market has been rife with crap. 3rd-party console controllers were equally sucky. Even Microsoft's PC controllers weren't that great.
These days, you could get by with a Logitech controller. But by and large if you want to game with a controller on a a PC you're going to use a wired 360 controller.