I think garrisons is the first really cool thing they have added in years. They should really have gone with one garrison per server and faction with benefits from each extra character of appropriate level you have though. It starts getting tedious pretty fast when you get a few level 100s. However, outside of garrisons there's very little to do except for raids. Personally I can't really stand raids any more, so I'm pretty much done with a character after a few of weeks just from doing one heroic per day. Challenge modes are not really a solution since they scale down your gear and are relatively pointless except as a means to gear up for raids. Maybe a better solution would have been to add a couple of more difficulty levels to 5 mans that you actually had to gear up for? That could add a couple of months for non-raiders.