Like I always say with these Bethesda games it's not really a matter of good/bad or right/wrong, but really it just comes down to a matter of personal preference. How close/far do you like 'content' spaced out, does fast travel annoy you or is it a necessity, do you need quest markers or do they annoy you, etc etc. Different people have different opinions on these things, and it will effect what you think about Morrowind/Oblivion/Skyrim.
Ultimately though, i think it comes down to a matter of CRPG vs WRPG. It used to be that an RPG on a console came from Japan - Final Fantasy, Phantasy Star, Suikoden, etc, while companies like Bethesda and Bioware made 'CRPGs' for the PC - Balders Gate, Fallout 1+2, Daggerall, etc. But with Microsoft entering the console race, these games came with them, and you had new types of RPG's on the Xbox like Morrowind, Knights of the Old Republic, and Fable. By the time we got to the 360, these games were becoming the norm and had undergone full on 'consolization'. The console became the primary platform, complexity through little used features were streamlined out (in TES case look at spears or medium armour), and many player conveniences were added in. For fans of older PC RPG's Morrowind was designed more for them, while from Oblivion on the games were designed more for the mass market. In my opinion that's really where the line is drawn for 'which ones best'.
I can't really blame Bethesda here and they're still all great games... but what I will constantly criticize them on, between Morrowind/Oblivion/Skyrim some game mechanics were adjusted and the graphics got better, but they're essentially the same game. Even Fallout 3 fits in there, as 'Oblivion with guns'. Then look at CD Projekt, and compare The Witcher to The Witcher 2, and now the upcoming The Witcher 3: Wild Hunt. Massive game changing improvements for each iteration. So when is Bethesda going to step it up and give us something that's a clear evolution over Morrowind? Right now there games could be categorized sort of like FFVII-FFIX in terms of improvements, but I'm still waiting for a true 'next gen' jump like we saw from Daggerfall to Morrowind.