Computer Chess. Where did black go wrong?

This is a new game played by GNU Chess against himself. I forced white starting with 1. g3 but the rest of the game was by the computer.

I assume white didn't play every best possible move, so I wonder what did black do wrong, or what better moves black could have done. The game finished a few moves later by checkmate by white.

My thoughts:

1. Black's move 12...g4! was very good.
2. Move 13: White did not capture g5 pawn because it leads to: 13.Bxg5 Bxe4, 14.Bxe4 Qxg5 Giving black material advantage.
3. 15...Qa2: we need to use all pieces to attack. Bishop and rook(h8) doing nothing, rooks are not connected. White is better in mutual co-ordination and position. Black's other pieces are not really contributing to attack. They are more defensively placed. Better could be 15...Bh6 or Nxf5 (f5 pawn proves crucial after the moves posted here.)
4. 23...Qxh2: All that can be captured should not be captured. Isolates queen from the game.

Did you yourself do any analysis?

Thanks for the interesting analysis, actually I hadn't even tried to do my own since I didn't know even where to start, but your post helps a lot and I'll try to go as further as I can from here now.

To begin with, you can pick up any game. After standard opening book moves, say 5-6 moves each side, try to guess next move. Then see what was actually played in the game. Both should match! Better if you pick up games with one side winning (not draw) and guess moves for winning side.

**If you are not playing, please don't use COMP vs COMP game. Use games played by GMs in actual matches.

A few sources to start with

--www.chessgames.com

--On youtube, search for Anand vs Topalov World chess championship 2010. Go through all 12 videos by user jrobichess (spelling may not be correct )

Thanks for the advice, I guess I used a computer game here because sometimes GM games have lots of moves I really don't understand, but I know I will learn much more with top human players.

Eventually, I found a couple of variations for black that could have been better, in one case getting a draw, and in the other achieving a more equal position for black and white.