I never played the original BG games. I don't think I played a lot of RTwP games. The only ones I've played recently were Pillars of Eternity and Masquerada: Songs and Shadows.
In both of those games, I found the RTwP combat to be pretty clunky because I had to constantly, CONSTANTLY pause the game to change what my various party members were doing, because with 3-5 party members and 4-5 enemies all roaming around trying to use abilities or melee on each other at once, almost all tactics attempted go out the window immediately.
RTwP is well, kinda crappy. With so many characters, the only way to play it is with constant pausing, and that's just inferior turn-based gameplay.