I will take a different approach on this hand. Please feel free to critique this. I think the river was played nicely. The check by the first guy was very sneaky and IMO very very tough to do sitting on the nuts in first position. Most players will make a callable bet to maximize thier payoff, rather than risking a free showdown. That being said, there is no reason to think that your hand is not good. You can pretty much rule out a higher pocket pair based on the betting, and like I said it is very difficult to put your opponent on a 9 since he checked the river to you. I would put him on a hand like 66 that went from very strong to crap.

(Another way to look at this is your opponent probably put you on a hand like QT or 78 that missed its draw, and felt like any river bet was going to make you fold and the best way to get more money out of you would be to check and let you take a stab at the pot, then come over the top.)