Well after playing for a while I can definately say the enemy AI is awesome. Firefights are definately challenging. The Germans will not just stand out in the open and trade fire with you. They'll always move and fire from a covered position. Once they're behind cover, it's very difficult to pick them off as they pop up to take shots at you. It's possible, but it will take time and ammo. The Germans will also change positions and try to flank you if not kept down with supressing fire.
You can order squad members to lay down supressing fire while you flank them or move to within grenade range. The same tactic is extremely important when trying to take a machine gun. If you try to take it out head on, you'll get mauled. It's also pretty damn hard to try to pick them off from a safe distance without a sniper rifle. Best thing to do with a machine gun is order your squad to lay down supressive fire while behind some good cover to draw the MG's fire. This will allow you to manuever around to either get behind it and take them by surprise, or get just close enough to lob a grenade into the MG nest. In many cases to have to go quite a distance to safely manuever around the gun.
I think that adds to the realism. All the maps are very open and allow several routes to move through unlike the MOH series with was pretty much just following a path. Anyway, I'll post more about it later, time for work.
