Grimrock still has a huge potential for novelties :
out of my head :
Spells:
Water Breathing
Wind Walk / Fly (can be limited by a special kind of resource, like spell component)
Terrain Modification (Lava, deals damage / Mud / Freeze Water)
Ceiling collapse (only indoor)
Teleportation and /or spell of recall
Switch place with target enemy
Most of those spell could be used for new kinds of puzzles
Combat:
Attacks that deals damage all around the party (Whirlwind or some such)
Spells that deals damage all around the party
Spells that deal AoE damage (3 x 3)
Spells that reflect damage or deal passively when attacked ( ala Shield)
Also spell combination with 2 wizards? Combo attacks with 2 fighters?
trap spell.
spell that weaken enemies (lower armor , speed , résistances)
Enemies:
Big enemies that take more space than a square (2 x 2?)
Or eventually that takes more that 1 vertical slice (think a Dragon in a cave?)
Enemies with weak spots (behind , side )
Or a huge serpent that block a tunnel - the party should defeat it several times in order to clear the tunnel.
Player race:
I supposed you don’t want to add standard fantasy races? Dwarves, Elves? or some anthropomorphic dog faced ?
Items :
traps (caltrops) to weaken enemies
Grappling Hook (as a mean to gain access to new areas)
Walking board to cross a chasm
well , I definitely hope to see a LoG III at some point
