The bishop exchange has emphasized Black's light square weaknesses, and his next move makes things even worse.

Eyeing the a5-pawn, with a huge positional advantage.

Preparing 2...h6 and 3...Bg5 to eliminate White's "good" bishop.

Getting on with the plan of b3-b4.

Avoiding 8...Nxe4?! 9.Nxe4, when White gets closer to achieving c4-c5. In the game Black keeps the important c5-square under control, whereas the bishop isn't really doing anything on e4.

Black has no problems.

Preparing Bf5 in order to swap White's good bishop. Besides this, there now appears the threat of ...Bxh3.

This weakens e4 for the rest of the game.

Exploiting the protected square. White's next move makes things worse, but his game was difficult anyway.