@engineer,
Just pursuing the idea of the knight sacrifice which I like more and more, I can see a couple of defenses for white, both not all that great. After 15.g4 Nxg4 16. fxg4 Qh4+, white can either block with the queen to keep it in play: 17. Qf2 Qxg4 18. Bxd6 Qxe4+
1. Nf3 Nc6 2. e4 e5 3. c4 Nf6 4. Nc3 Bb4 5. Nd5 d6 6. Nxb4 Nxb4 7. Qa4+ Nc6 8. d4 Bd7 9. Qc2 0-0 10. Bg5 Nxd4 11. Nxd4 exd4 12. Rd1 c5 13. f3 h6 14. Bf4 Bc6 15.g4 Nxg4 16. fxg4 Qh4 17. Qf2 Qxg4 18. Bxd6 Qxe4
or move the king: 17. Kd2 Qxg4 18. Bxd6 Bxe4+ with white's rook hanging and the queen out of play.
1. Nf3 Nc6 2. e4 e5 3. c4 Nf6 4. Nc3 Bb4 5. Nd5 d6 6. Nxb4 Nxb4 7. Qa4+ Nc6 8. d4 Bd7 9. Qc2 0-0 10. Bg5 Nxd4 11. Nxd4 exd4 12. Rd1 c5 13. f3 h6 14. Bf4 Bc6 15.g4 Ng4 16. fxg4 Qh4 17. Kd2 Qxg4 18. Bxd6 Bxe4