Hey guys, I'll admit I burned out pretty hard on Midkemia. I played it a lot over the course of two months and in that timespan, had a lot of dramatic RP, climbed near the top of the PVP world, leveled my character up to a very high level (no level cap), got rich, got an insane weapon, have two classes and even a mount that nobody else in the game will ever have. So after pretty much "doing everything there is to do" in Midkemia, I got kind of bored. But you know what? I came back. I tried Heroes of Newerth. I tried Skyrim. I tried Star Wars: The Old Republic. I tried finishing Mass Effect series. I tried Diablo 3 and Starcraft 2. None kept my attention as long as Midkemia did, and in none of them did I experience the range of emotions that I did in Midkemia.
So I thought about it (because I don't want to burn out again) and I figured some things out for keeping yourself from burning out. This can be applied to pretty much anything - from other MMO's, to RPG's, to whatever.
#1 - moderation is key. Don't play 16 hours a day. This seems obvious, but it can be difficult if you have a lot of free time and there's always something your character needs to do to 'get bigger' - such as gathering in traditional MMORPGs, bashing in Midkemia, whatever. Make a limit if you need to.
#2 - keep goals for yourself, but don't dedicate your existance to meeting them. This can be reaching a certain level, getting good at PvP, getting a certain rank in exploring the game-world, whatever! Main thing is, have something to work for. Just don't work towards it so much and so often that you reach your goal within 3 days. This will keep you interested, without running out of things to do (which is surprisingly easy to do, even in games like SW:TOR).
#3 - find a good rival. This is someone who is about your skill level in whatever you're competing in - be it politics, RP, PVP, whatever. It's also preferable if they get better at the same rate as you, too. If you constantly have a friendly rival, you'll constantly have reasons to improve. Just keep #1 in mind.
Hope these help, and if you haven't already - come try out Midkemia! There's even a neat little link there for you.