Of course there are other options here. Against 4...e6, White usually tries to prove the advantages of not having the knight already developed on c3, although I have never quite understood what those advantages are. In any case, the Black players can hardly resist the temptation to develop the c8-bishop, something they cannot do most of the time in the normal lines of the Semi-Slav Defense. The other very popular option is 4...Bf5, and that was usually my choice back in the days when I played this variation.
1. d2d4  1... d7d5  2. c2c4  2... c7c6  3. g1f3  3... g8f6  4. e2e3 When I was a tournament player I loved playing this opening with both colors. It leads to the kind of long-term strategic battle that I've always enjoyed. That's exactly what we'll see in this game.