As a fan of Magic the Gathering and D&D, I enjoy general fantasy monsters as well. I just think that that those monsters fit better into games of other universes like D&D or LOTR. Yes, this is mostly opinion. I do feel, however, that it is a stretch to call opinion the assertion that Morrowind had a far more unique set of monsters in comparison to other fantasy settings than Oblivion. I feel that this uniqueness and sense of exploring a world full of new, unknown creatures is more compelling than fighting the same creatures that have been around for decades. What is the point of creating unique lore for a world if you aren't going to fill it with unique creatures?
:shrug: I agree Morrowind had a more unique monster types. I however just don't think its my cup of tea. I'd rather fight those general fantasy type monsters in first person to experience those epic battles with the same beasts you always read about or watched your avatar fight pixalized representations of. That's really cool for me, when I can pick out what a monster is from other stories, and while I'm fighting it I can think how it is to go toe to toe with a minotaur.
In Skyrim I expect monsters that fit the landscape. Sure a floating jellyfish was interesting to fight for sure, but it would be kinda strange to find one in Cyrodiil. Cyrodiil came off as a more general fantasy level area, so I would expect general fantasy monsters. Skyrim is more snowy but still lower fantasy, so I expect monsters that are low fantasy and fit the area. Like mamoths and saber tooth tigers, or snow vampires.