I watched Tron Legacy a few weeks back. IMO it was average. Graphics was stunning, I can't really compare it head to head with Avatar because they focus on different things. But I must mention that unlike Avatar, where a whole new world was displayed, the landscape in Tron was more or less the same, although the glittering bright colours glowing in the overall dark setting was very appealing, my eyes got a bit tired in the end.
As for the sound effects/music, Tron Legacy gets a perfect score. The electric music by Daft Punk matched the theme perfectly.
Nevertheless, I felt the plot was too flat. Maybe it's because I didn't see the original Tron movie, but I think that the relationship between characters wasn't well established, especially between Sam and his dad. Their relationship just seemed too weak to me.
Overall, Tron Legacy was worth watching, but the plot could have been better. After all, I really had a lot of expectations for it