I'm not sick of any series, as such. There are plenty I'd never touch with a pole and which I always walk away when my friends bring them up ('I like so totally got a 360 noscope on Battlefield- hey, wait, where are you going?') though thats more to do with having friends who often have little else to talk about. Its that or their girlfriend problems, so I guess I'm lucky.
Basically, if there is a series, like CoD, which seems to have been milked to death, then I'll either not buy it or buy every third game or something, so I get a bigger development gap for less cost. I'd never want a series to end as long as people are enjoying it- I mean, I like Pokemon and it irritates me a little when people say it should stop being made- because then I'd not get to play the new ones.