Qxg3 (forced move), ..Ne2+(forks queen with check!), Kh1 (the only move), ..Nxg3+ (takes the white queen and again gives check) and white cannot re-capture the knight because that would open the f-file and ..Rf1 mate, so Kg1 (forced move), ..Ne2+ (check again, and clears the third rank for the rook), Kh1 (the only move), ..Ra3 (moves to safety and attacks pawn), and black would still be a piece up, like this:
I agree this is an amazing move to get the queens off of the table, but it actually gets the queens and half of the rooks off of the table. Instead of the second Ne2+ move, White could play Rh5. This attacks the hanging rook at c5, forcing the trade and allowing the knight to escape safely on the recapture.
Taking the knight with fxg3 would be even worse for white, as he would lose both rooks in exchange a rook & knight.
It is an amazing move!
try the immortal game