My best chess game(Against the computer)

Playing against Arasan 5.2 I notched up this impressive win.Arasan's ELO is around 2000 to 2200 which means that it is much weaker than a Grandmaster but much stronger than an average chess player.
I love this game as this game shows the strategy required to beat the computer in its own game.The key is the suprise move,as the computer can compute far more nodes in a second than you can probably in your whole lifetime.
The game goes(French Defense,Exchange Variation)
1. e4 e6
2. d4 d5
3. exd5 exd5
4. Nc3 Qe7+
5. Be3 Be6
6. Nf3 Nf6
7. Be2 c6
8. O-O Nbd7
9. Ne5 O-O-O
10. Bf4 Nxe5(see picture)

11. dxe5 Nd7 (Why not Bxe5,the answer the Rook and the Queen is in the same diagonal,potential to a attack from the Bishop)
12. Qd2 Re8
13. a3 Bf5 (if not a3 then Black could have played Qb4)
14. Rfe1 Qe6
15. Bd3 Bc5
16. Rac1 Be7
17. b4 Qg6
18. Qe3 Nb6 (the a7 pawn is a easy bunny without support,see picture)

19. Na4 Nxa4 (Knight Sacrificed to gain superb position,computer should have rejected the sacrifice)
20. Qxa7 Kd8 (forced, if king does not move then
20.Qa8+ Kc7(Kd6 follows e6 threatens mate and Queen is lost)
21.e6+ and mate follows)
21. Qxb7 Qe6 (why Qe6 why not Ref8?)
22. Bxf5 Nc5 1-0(picture)