Not turn based, and real-time-with-pause combat doesn't work for me, to the point where I consider it a dealbreaker. (As I said before, RTwP is worse than either turn-based or full real-time.)
bioshark: Haha, let's agree to disagree. For me it's the other way around. I really enjoy real-time-with-pause combat. That's how I played BG I and II, IWD, etc back in 2000 and in my opinion the system works great.
On the other hand I really hate turn-based combat for this games. For me turn based combat is Heroes of Might and Magic series...
It's all good when everybody can play their own game in their own way.
Here's an explanation of why I don't like real-time-with-pause:
Turn based combat has a nice rhythm to it. You enter your command(s), and then you get to see the commands execute. (Of course, your enemies also get to act in turn.) Also, with turn based, you're not in a rush, and even if an emergency situation occurs, you have plenty of time to think about how to solve that emergency. (It can still be stressful, like when a player of a roguelike is about to lose next turn and is frantically searching their inventory for an item -- any item -- that would get them out of that situation.) Also, turn based games have an accessibility advantage; players with poor reflexes can easily enjoy such games without issue.
Real time combat, on the other hand, is quite fluid if done well. (With that said, real time combat doesn't work so well when one player is controlling multiple characters/units; I find that real time works best if the player is only controlling one character, if it's a multiplayer game with one player per character, or if it's a character-free game like Tetris.)
RTwP combat, on the other hand:
* Lacks the rhythm of turn-based because pauses are irregular. Also, there's the fact that a player can sometimes lose just because they didn't pause the game fast enough.
* Lacks the fluidity of real-time because the game is constantly being paused.