What about a Witcher-like system? having three different perspectives(High Isometric, Low Isometric and Over-The-Shoulder) is quite useful. People who prefer using the mouse to move around could play the game in either high or low isometric view. Others, who prefer using WASD(or the arrow keys) could use the OTS-look.
I prefer the OTS look, but the isometric view comes in handy when you're fighting multiple enemies.
If the game has real-time combat, IE aiming and shooting arrows, I'd prefer an Oblivion like system, where you're able to switch between 1st and 3rd person views.

[Linked Image from miniprofile.xfire.com]