I agree with almost everything here. The side quests made this game for me. Even after numerous replays I STILL haven't finished the main quest because I'd spend all my time doing side quests or random jobs for random npcs, exploring, fighting, tomb raiding etc. After several months I'd get a bit bored and move onto something else and remember, a few weeks down the line, that I had to go back and do the main quest. How long has this game been out? Sheesh.
Having said that, I hated the levelling concept they implemented for the game. The combat was awful and it pissed me off no end having to back peddle 7 miles whilst firing arrows at some monster just to bring it down. And then repeat ad nauseum. It made my style of play totally inefficient and worthless.
Now, Fallout: NV - that is a game that has given me a raging nerd on for the last 3 months non-stop. If anyone plays that on PC then I recommend they look for the New Vegas bounties mod set because it is almost like being back in the Dark Brotherhood guild. Except you are a good guy / gal.