Bishop Sac on 15. Bxg6

Lately I've been making the unexpected moves (and apparently the better moves) and got my rating up over a 100 points in the last several games. In this game I routinely avoided the expected trade offs that he kept offering and continuously shook the game up, culminating on move 15. Why he didn't capture the bishop on ...15 to make it a true a sac is beyond me. Or was there a reason not to capture the bishop, for instance he was afraid I'd force a draw with ...15xg6  16. Qxg6+   ???

Nice game, some comments.

a) I think 8.exd5 would have been much better for him. The resulting position provides black with a beautiful square on e4 and possibilities to attack your center with 0-0 and Re8

b) Him playing f6-d5 was too weakening I believe, and led to the attack down the diagonal.

c) Playing without the castle was risky, and could have backfired. For example there is a funky line given by the CPU: 10...Nxf4 11.exf4 Nxd4 12. Nxd4 Qxd4. Very hard to find but just to illustrate the point.

d) Nice of you to find the sacrifice. It was a very well executed attack despite his mistakes.

I would probably have played the simpler 15. Bc4.

15 Bc4

My ultimate shortcoming is that I dont' expect people to make such blatently terrible moves since I very rarely do the  myself. So many times I catch myself missing such moves just after I make my move.

A lot of times it happens that way though. The better choices only appear to us after we complete a not so good move. And perhaps here Bxg6 looks quite enticing since it breaks open Black's pawn shelter, which is probably why you opted for 15. Bxg6.