You won't have a bad meal...but you may not remember it. That's the problem. In my opinoin it doesn't live up to its Four Seasons name. It's not a memorable hotel fine dining experience (a la The Dining Room at the Ritz Carlton), and it's not even a destination restaurant. Instead, "Seasons" (that's the restaurant's name) presents more as an upscale grill, like the Four Season's more contemporary interpretation of Ruth's Chris but with a few pastas thrown in for variety.
I have eaten in the main dining room probably 6 times, and I've had very good but uninspired meals there. The only things I remember from all of those experiences are (a) the breads are delicious and housemade, and (b) their ice tea comes with ice cubes made out of tea so that when the ice melts your tea doesn't get watered down. Honestly, that's all I can tell you after at least 6 meals there.
Actually, in my opinion, the best dining experience at the Four Seasons occurs in their bar. Pull up a comfy chair, have a beer or glass of wine, and order a cheeseburger off their bar menu. It's truly one of the best, juciest burgers in SF.