Not everything is for everyone. Personally I'm enjoying SC2, but there have been plenty of great games I just couldn't get into (Arkham Asylum comes to mind) so to each their own.
What I would like to point out is two things, first that the 'everyone plays their own game' thing has been sort of done in the past already, Planetside allowed you to play as a frontline soldier, a mechanic who kept the base running, a pilot whizzing about, a tank driver maneuvering through a battlefield, or a small team of commandos infiltrating the secure facility. It was far from perfect, but it worked pretty well and had a good blend of different gametypes. I don't know of another game that allowed you to go from commander (platoon leader, you could only give directions and set waypoints but that was almost always enough, especially if it wasn't a pick-up group) to commando (infiltrating and wrecking the enemy facility) in the same game during the same play. It can work, and it can work well.
And yeah, the RTS commander+FPS soldiers thing has already been done quite a few times, and in some pretty big name games. Battlefield 2142 had a pretty good balance IMHO, though the Empires mod is also pretty good (Battlefield tends to have more focus on the FPS, with the commander aiding the soldiers, whereas empires has more focus on RTS, with the commander building all the tech, weapons and armor).