OldOldGamer: Cartoonish graphics is a start.
The environment lighting is too colorful and cheerful: blue, green and generally realy reminds of hack-and-slash dungeon crawler.
Huge, immense, caverns don't help in providing that claustrophobic feel. Randoms chains hanging from the ceiling are just cheap.
I don't know the "cartoony" look was there in the originals too (and it's not just UU, most Ultima games had very cartoony graphics too) and, at least in UU2, there was some huge areas too (within the realm of the period technical limitation), If anything you could say it's more reminiscent to it's predecessor than it would be with photo realistic graphics .