Gilmoy: This game is theory through 20..Rd7, with 11 games in the database, evenly split +4-4=3. Even the Q sac is well-known, apparently dreamed up over-the-board by Ivanchuk in Ivanchuk vs Shirov, 1996 -- read that page for some good analysis.
White's 21st moves in the database are:
21.Qg7 : +2-2=2
21.Qd4 : +1-0=0
Tactically, Black's advanced Q-side pawn wall cuts both ways: it's closer to queening (which is usually how Black draws or wins), but meanwhile, Black's K is badly exposed on two diagonals. White's 17.a3 rips open the a-file, and 19.Be3 is a hidden double on weak a7.
19..Nc5 throws down the gauntlet, closing the diagonal and daring White to try the Q sac. 22..Bxg7 hangs the N, so White is trading his Q for B+N, with additional threats like Bh3 and Rxa7, plus the two tempi for Black to deal with the g7-pawn.
This is the only Q-sac game where Black didn't continue 23..Rg8. 26..a5?! is a brute-force attempt to "save" his a7-weakness, but after 28.Bf1 the a-pawn falls anyways, and White's R+BB penetrate into Black's quadrant, e.g. Rxa5-Ba6-Bf4. Black's pawns are stuck, and the g7-pawn is paralyzing his back R.