I'm not going to pick sides until I play Daggerfall and Morrowind, which I plan on doing whenever I get to them. Currently I'm playing Arena (7 or 8 months), Oblivion (since 2008), and Skyrim (since 11/11/11). I have heard plenty about how the second and third games of the ES series have loads more content than TES 4 and 5, and for this reason the latter games are 'dumbed down', but it's not fair for me personally to say what my opinion is until I've looked at all the series.
Personally I dislike the term 'dumbing down'. It's one of those gamer terms (like 'broken') that doesn't truly fit. Also, one of the things gamers often do when comparing new games to old is they talk about all the content which was in older games that is now missing. And then they start criticizing, downplaying, or just plain ignoring anything new. To get a fair view of anything, you have to consider all points of view. Just because the haters don't like something new (which is often the case) doesn't mean that it's not appreciated by other gamers.