Interesting city, not particularly well setup for the English speaking tourist - but you are in Russia after all! It's very spread out, so be prepared to do a lot of walking, or get used to deciphering the Metro station names. Overall, a pleasant 3 days and a must see on any avid traveller's list.
Insider Tip:Be inside the Kremlin at midday on a Saturday. They put on a special military demonstration for about 45 minutes - marching band, horses and foot soldiers. Extremely entertaining and included in standard admission fee.