I've never felt comfortable with the chess positions that arise in the Grünfeld Defence. After the usual exchange variation moves, 1 d4 Nf6 2 c4 g6 3 Nc3 d5 4 cd Nd5 5 e4 Nc3 6 bc c5, games tend to take on a more open character than is typical in queen's pawn openings.
White tries to maintain his impressive centre, using it to first restrict and then drive Black back. Black on the other hand looks to prove the centre is overstretched and tries to gain a strong outpost at c4. Initiative is important, as is a knowledge of endgame strategy as games often develop into a queenless battle between White's central majority and Black's on the queenside. More frustratingly for the amateur player is that early subtleties in White's queen rook positioning can make dramatic long term differences to the outcome of the game.
As we saw in the Karpov - Kasparov game posted earlier today, a single innacurate move can lead to exchanges and no further chances to drum up winning chances.
Kasparov's adoption of the Grünfeld, he used to play the King's Indian until Kramnik posed him a lot of difficult questions, led to a resurgence in the defence. Interestingly, it is an opening that increases in popularity as the strength of the players increases; it seldom features in lower club level games.
Occasionally, swash buckling attacks can occur in the Grünfeld as this game between Polugayevsky and Kudrin shows (this is the line I'd tried to play against Israeli GM Eran Liss, but was badly mauled):