Villan is a decent reg:

Full Tilt Poker No-Limit Hold'em, $4 BB (6 handed) Courtesy of

CO ($640.80)
Button ($74)
SB ($864.80)
BB ($568.10)
UTG ($382)
Hero ($434)

Preflop: Hero is MP with , .
1 fold, Hero raises to $14, 2 folds, SB calls $12, 1 fold.

Flop: ($32) , , (2 players)
SB checks, Hero bets $24, SB calls $24.

Turn: ($80) (2 players)
SB checks, Hero checks.

River: ($80) (2 players)
SB bets $66, Hero raises to $175

I don't see what hand he can have besides 88 33 or AQ unless he is bluffing river. I cant see what he bets river there. I mean he expects you to call with 8x??
I wouldn't be surprised to either see bluff or set that planned to CR you on turn.
But you say that he is a decent reg..So a decent reg should not have Ax there often. Maybe 10% of the time is he is trying to mix up his game by cold calling AK AQ for shania and such. Just as to have wider hand range.
And i cant see him having Kx there...Unless he is floating flop with no outs.
Actually a decent opponent should have set there almost always given the action. I'm sure that many of you will disagree with me but I guess that you raise in MP A7s+ ATo+? and all PP's? Given that I will have Ax or set there over 40% of time and will double barrel enough to make sure that floating with pocket pairs will not be profitable. Then If he actually cold called a strong ace and such 2 turns came i guess that he would try to get to cheap showdown unless he thinks that you are total donk and will call him light.

I agree with gsdavid about that he should have a decent A there. I'm not sure about the set alternatives, it is possible his intention is to get you to bet your A on turn so he can CR his set. Anyway I think its a bad line to take with a set because against a good player I would check turn behind wtih TPTK often enough on this board.

I think I like the river bet, he should fold his A, medium PP etc often enough to be EV+.