No matter how good you are, there is always someone better.  I am glad you found some really top notch people to work for you!

Now, do what you enjoy!

Game design may just have outgrown you.  Imagine being a movie maker in 1920 -- you point the camera at a stage play, it doesn't start on fire, you're a genius.  Then all of a sudden you have to do cuts, sound cues, makeup... Suddenly you suck at movie design compared to someone who learned from Citizen Kane instead of the radio.

How many years was it before anyone even realized Monopoly was a bad game?  And then you had impossible games like Ghosts 'n' Goblins and incredibly vague games like D&D.  Now, if you look at World of Warcraft, Farmville, or Mark Rosewater's columns on dailymtg.com, you can see theory developing and human psychology being plumbed every day.  It's like the difference between oatmeal and Honey Nut Cheerios, or carrots and baby carrots.

Try Civilization: Revolution on your iPhone some time and compare it to original Civ where you could have about two units per city and you'd have to reload if you lost a battle.  Look how they added in things to reward exploring like the landmarks and the wonders, things to reward building with culture, things to make cities special with Great People.  Plus achievements.  You design fine tobacco products; but they've invented crack pipes now.

It's ironic that I often am good at things I don't always enjoy and suck at things I do. But those times when I am good at what I like can usually make me feel good enough to ignore the rest.