When deciding upon a repertoire to meet 1 d4, those players whose natural inclination is to be aggressive have a difficult decision. There are plenty of outright counter-attacking tries such as the Benko Gambit, the King's Indian Defence and the Modern Benoni. However, such openings are generally considered borderline unsound at the higher levels. On the other hand the safe options such as the Queen's Gambit Declined and Queen's Gambit Accepted make it difficult to create middlegame complications. So, what to do?
Play the Semi-Slav! (1 d4 d5 2 c4 e6 3 Nc3 Nf6 4 Nf3 c6). This line provides a great balance between solidity and dynamism. The opening is undoubtedly sound but also contains plenty of latent aggressive possibilities. The Semi-Slav is also one of those openings that will repay players who enjoy studying the game. The lines are intricate and the player who is better prepared will have a substantial edge.