If you're not taking kids, I'd skip it entirely. We liked it and I'd do it again, but only because (1) it was a character meal on our first night, and (2) we had kids with us.
While the food was good (not memorable, but absolutely palatable), I really just didn't care for the over "feel" of the restaurant. Mickey and friends were fun, but you can get them at so many other places outside of this restaurant.
If it were our first night at WDW and we planned to spend it at Epcot, I'd definitely consider it a second time. But, honestly, only if I were taking kids because the only real draw for Garden Grill - in my opinion - is the characters.
There are sooooooo many better places to consider at Epcot. If you'd like your first meal to include characters, then I *strongly* recommend Akershus. They have the princesses and the food is good enough to stand on it's own. We also LOVED Biergarten and Tutto Italia.