Assume the game was equal until move 28, white had attacking chances and a draw at least. But white made a blunder 28.Nf1??, if 28.Bf1 was played, then the game can continue in this way:

2bqnrk1/5p1p/5PpQ/3pP1P1/2pP1R2/2P3N1/6BP/1q4K1 w - - 1 28

1. Bf1 Qd1 2. Rh4 Qh5 3. Nxh5 gxh5 4. Rxh5 Bf5

The game is almost a draw with some minor advantages for black. It's ambiguous.

But white played 28.Nf1?? and black put his queen on e1 to capture the white's rook on h4 -- a big material advantage for black.

The game was ambiguous until move 28, there is no clear way to win but as you mentioned white has the attacking form.

Let see the game from move 18.e5

2bqnrk1/5ppp/r7/pp1p2P1/2pPP3/P1P2PN1/R5BP/2Q2RK1 w - - 1 18

White is attacking on king's side as Kasparov mentioned he could play 18.Rb2 to avoid black to make a passed pawn and keep pressure in both king and queen sides. But white decided to complicate the game.

Another move which leads many people criticize Anand was move 20.axb4

2bq1rk1/2n2ppp/r7/p2pP1P1/1ppP1P2/P1P3N1/R5BP/2Q2RK1 w - - 0 20

1.f5 b3 2.Raf2

Some GMs and also engines prefer to push the pawn to f5 and continue attacking just in king's side. White's 20.axb4 made a passed pawn for black on square b3 (two moves to promote) and black got counter play.

Before move 28 white had attacking chances and a draw at least. But white made a blunder 28.Nf1??, if 28.Bf1 was played, then the game can continue in this way:

2bqnrk1/5p1p/5PpQ/3pP1P1/2pP1R2/2P3N1/6BP/1q4K1 w - - 1 28

1. Bf1 Qd1 2. Rh4 Qh5 3. Nxh5 gxh5 4. Rxh5 Bf5

The game is almost a draw with some minor advantages for black. It's ambiguous.

But white played 28.Nf1?? and black put his queen on e1 to capture the white's rook on h4 -- a big material advantage for black.