Recently, a friend asked me how I can still get excited about pen and paper roleplaying games, when we've largely been playing with the same systems (and even mostly the same group of guys) since high school. I had to think kind of hard about this one, since it's not something I really have given much attention to. I've never been burned out on RPG gaming in general, though I have had to take breaks from certain aspects from time to time.
I think the answer is just that. When you start getting that 'too much of this...' feeling, try something different. I took a break from the 'Adventures of Bjorn Shepard' series, even though it was wildly successful, just because I didn't want to force it and get sick of something that I loved. The same goes for Fantasy RPGs, which I leave and come back to at fairly regular intervals.
Most of us have pretty broad interests when it comes to media. We like sci-fi, we like horror, we like fantasy, we like disaster movies. Why pigeon hole your gaming to one flavor when you don't do that with any other facet of your life. Have a little variety. A spoonful of sugar helps the medicine go down. When I start feeling worn out on a setting, I switch. Or read. Or play more video games. Actually, a lot of the problems in my life are dealt with by playing more video games.
Now before I get too preachy, I'll address the elephant in the room. The reason I have this developed theory about why I don't get stuck and burned out in RPGs is because exactly that happened with tabletop wargaming. I'm not going to place blame here, but I blame 40k...wait. Actually, it's my own fault. Despite knowing all of the above as it pertains to gaming and life in general, I got into 40k really hard, and played it as pretty much my only miniatures game for a few years. Then, when I got kind of tired of just what was going on in 40k, instead of taking a break, I tried to plow through. Throw in the convenient timing of a price hike and new edition, and something had to give. Still and all, I mostly pay attention to what's going on in 40k, though it might never be the same for me as it was.
So, for anyone who was interested, take that for what it's worth. Also, remember, the best thing to do with advice is just ignore it and do whatever the heck you want anyway.