Two for me, is that allowed?
Oh, and one of them is a whole series?
One is the entire Outlaw series. I picked those games up for less than nothing and they were sexist, crude and entirely unfunny. They were also some of the most entertaining sports games ever. I STILL play the tennis and got hours out of the golf. They had stat building, lots of unlockables, tons of creative modes, Dave Attell and Stephen Colbert. Heck yes.
The other one was Culdcept Saga on the Xbox 360. I'd never played Culdcept and when my boss introduced it to me I was immediately hooked. Of course, I think he and I are the only ones I know who have ever liked it.