These are the only three I've played, so I can't compare versus the ones before Morrowind.
People always enjoy looking back on the older games, in any series, unfairly fondly. When Grand Theft Auto: San Andreas came along, it was said that the game was crap relative to the wonderful Vice City. Then once IV came out, San Andreas was suddenly the most amazing game in the series. With Forza Motorsport 4, FM3 was often sited as better, but two years earlier when FM3 came out it was said that FM2 was better. Any given The Legend of Zelda game is compared against Ocarina of Time and OoT is always regarded as better. With The Elder Scrolls we see the same, with Oblivion having been said to be inferior to Morrowind, and now we're doing the same with Skyrim.
The more recent Elder Scrolls games haven't simply improved over Morrowind in terms of aesthetics like prettier graphics and voice acting. This generation's Elder Scrolls games made some critical improvements over Morrowind in other departments as well, including the improved combat mechanics and dramatically superior menus including better organized lists for stuff like ingredients and an infinitely superior quest log. As I recall from playing Morrowind on the original Xbox, my quest log was simply done like a series of notes in a notepad all in chronological order rather than being arranged together with relevant information. This meant I would often have to browse through a dozen pages of journal notes looking for the one piece of information I need. If Morrowind, Oblivion, and Skyrim all came out today at the exact same time for the very first time (pretending Morrowind and Oblivion had not previously been released), and all three running Skyrim's graphics engine and all three with full voice acting (as I recall, not all dialog was voice acted in Morrowind), but otherwise each being just as they really were including retaining the same combat mechanics, menus, and features, nobody would insist that Morrowind was better.
The same goes for movies. People seem to enjoy talking about how much worse remakes are versus their originals, but if the originals and the remakes had appeared side-by-side for the very first time (rather than the original having been released years earlier) almost none of the originals would be favored over their remakes. The remake of A Nightmare on Elm Street would be favored almost universally, the remake of King Kong would be universally favored over the original (not just because the original was in black and white and graphically primitive), and the new Halloween (Rob Zombie) would beat the crap out of the original, just to name a few examples. Yet somehow everybody always remembers the originals as so much better somehow.