Tactics do play a huge part in this game. I always try to maneuver my units to attack on the flanks because it breaks the enemy quicker. I also spend awhile studying the terrain before deployment because that can make the difference.
I'm playing as Prussia right now and am constantly in a state of war. I had, at one time, Poland-Lithuania, Austria, and Bavaria at war with me, which really stretched my army thin. I just captured Vienna, but the Poles retook Warsaw. Very challenging game. I've dedicated most of my technology research to the military... I just got fire by rank, which absolute decimates the enemy, and square formation is top class against cavalry charges.