The GTA engine is one which I explored the possibilities of for use in my 3D game..
Sadly, the GUI is *not* possible to make it function as per in Zelda with any sort
of 'easy' success without an insanely good coder.
If you have a good coder- I wish you an incredible amount of luck though, :-)
because it would be a *very* good engine to work with for the purposes of
Zelda.
Personally I hate the GTA series, but the engine is rock-solid.
It's much like the Oblivion or Morrowind engine- both are also great candidates,
for obvious reasons, but you ***cannot*** get rid of, or make invisible completely
the rpg backbone of the game (meaning the whole stats/classes/etc aspect)..
One could argue for NWN engine- but once again, it's a case of the underlaying
programming that is ***NOT*** fully removable without breaking the engine,
that is the problem.
I'm sure with a great programming team that any of these engines would be
great for obvious reasons, but without one- and I'm talking a *seriously*
dedicated programming staff-
I just don't see it as viable.
Now, For the GTA engine- it would be very easy to get everything except
the heart system into it, but I personally feel the heart system is too pivotally important to
ditch just for the sake of 'easy development'..
You could fairly quickly make one heck of an awesome mod with it, with a couple of good
modelers. It could be seriously, seriously epic. But- you'd be sans the heart system...
My 2 cents.