[diconoclastx]

Thanks for all the replies. I called his river pot sized bet. My reasoning was that if he had a hand like KK or QQ, he wasn't going to call a raise. From the betting sequence, I thought a lone ace for my opponent is unlikely, and it is more likely he had AA (say more than 50%) or a pure bluff, and I would lose more money in those cases. It turns out he had AJ, and I felt I had lost a lot of value.