The first d&d game i played was Baldur´s gate. I loved the story, loved the magic weapons (Divine Fury was the best sword EVER) and mostly loved how your commpanions interacted betwen each other.
Of course Baldur´s gate II and Icewind Dale were great too, but then came Neverwinter nights and even though i lked it there was something amiss, like it was not the same.
In those 3d games it became more evident the lack of Y axis. No jumping, no climbing no flying, etc. That made spells like Flight, spider climb or jump impossible.
Now you must be thinking "Ok, we got the point, you want more"
Yes, i do. And i have examples of different games.
Morrowind: Yes, morrowind and not Oblivion. Morrowind was more versatile than Oblivion (you could even wear a heavy armor gauntlet in your left hand and a leather globe in the other. Pointless, yet fun) Plus, you could fly and create your own stuff. (artificers, rejoice!)
Thief: God, if you like the rogue class this is THE game for you. Hide in the shadows, lift your unconsious or dead enemies so they would not be discovered by other guards, shooting water arrows to candles and create more shadow areas to hide, etc.
Prince of Persia (any): Jumping, climbing, running on walls, this game had a lot to offer. Basically, it was the first parkour game in history.
Overlord: Not the best game if you like to face your enemy by yourself but one of the best example for a summoner to control his/her minions.
Batman Assylum: I like how the cape moves...
Perhaps there are games now on days that already have all this but not D&D games. Imaging a game like morrowind, where you could hide your face with a mask and guards didn´t chase you even when you had a bounty on yourself (changelings would be fun to play). Mages and artificers could buy a house or build a tower and set themselves a lab where they could create magic items. Rogues could actually have a mission were they could steal items and getting no bounty if there´s no witness. Items like the Rod of Rope (complete scoundrel) would be invaluable for acrobatics characters. Rangers creating their own arrows, Druids shapeshifting, customizable outfits, bracers, belts, capes and rings that are visible in your character when you wear them, wizards and sorcerers using spider climb to stay out of danger or casting Mordenkain´s magnificent Mansion just for fun, fighters that... well, fighters would still hack and slash, but they would be cool doing it.
And the only reason (well, not only but mainly) we don´t have this game is because developers face it like a d&d game and not like an adventure game.
I really think THIS game would be the best d&d game ever made.
P.D.: Hey, never said it would be easy!