Personally I've always felt that the main plot is the meat, side-quests are the fix 'ems, and the bread counts for graphics and controls. If you're sinking your teeth into a really great steak sandwich you're more likely to finish it off even if the bread has desintigrated into a pile of juice-soggy scraps in your hand. Conversely, I'll always feel more than a little disappointed if you take a great herb-and-cheese bread and slap on a slice of ham so thin the pig didn't feel it come off his ass.
My point (finally) is that sidequests should be more than filler for a world. The should offer up activities you can't do during your main quest (or don't allow you to do often enough). They should give you unique sites to explore, unique puzzles to solve, and it should have an impact on the main story's progression.
My point (finally) is that sidequests should be more than filler for a world. The should offer up activities you can't do during your main quest (or don't allow you to do often enough). They should give you unique sites to explore, unique puzzles to solve, and it should have an impact on the main story's progression.