enoughsaid05: White's choice of moves leaves himself a bit tied up.
4) ...e6, 5) ...d5
Tal prepares to challenge the centre. White then faces the dilemma.
If White chooses to capture, then
6) cxd5 exd5 7) exd5 Nxd5
If white chooses not to capture, Tal's black knight in the centre of the board leaves White a losing game.
8) Nxd5 Qxd5
And white faces a trouble. His light square bishop is blocked! Clearly 9) d4 Nxd4 and black is winning. But if he does nothing, his knight will one day occupy d4 square, leaving white unbearably crammed. Even if white chooses Be4, followed by Bxd4, cxd4 and white is quite doomed.
As we can see, throughout the game, Tal is keen on having his c pawn remaining in the game. He is going to use this as his outpost to support his minor pieces for attack.
For the past few moves, Tal finally makes his way to Nf5, hitting the d square again.
Tal is not letting up any chances (d4 with the intention of capturing the c pawn with hope of any chance of counter play). Besides, he is opening up the d file to provide even more support for his knight to the centre. Brilliant isn't it?
Tal is keeping his options open. Here he has two knights that can go to the centre, Nbd4 or Nfd4, judging by the position, it is better if Nb4 with the idea of Nc2, increasing pressure on white.
White is quite doomed by the way. The rest is all tactics.