A bigger issue in that a lot of us consider Skyrim a great game...but not a great RPG, let alone a great TES.
Bethesda has progressively stripped the RPG elements from the Elder Scrolls games, and that's a lot of whats issue. We've lost attributes, brithsigns, character classes, meaningful differences between races. We have less player choices, and less variety or diversity in the characters we interact with and the organizations we can be apart of. So from that standpoint a lot of people criticize Skyrim, and have been disappointed or unhappy with it. This should be be confused with complete discontent though - I paid 60 dollars for Skyrim on 11/09/11, I preloaded it in 11/10/11, and I started playing it on 11/11/11 and did so for several weeks. According to Steam I have 165 hours invested in it, and without a doubt it was worth the money - I enjoyed the game. That said, I feel that the game could've been five times better had they stuck more to the principles they used to make Morrowind, and cared more about improving existing gameplay than trying to reinvent the wheel. These criticisms are aimed not at tearing down Skyrim, but in hopes that they build up the next Elder Scrolls so that it better conforms to our ideasl and expectations.
By example, I'm of a differing opinion.
I've played since Daggerfall, and I see each game as a natural and well planned out evolution of not only the series, but of the aspects of the game that make an Elder Scrolls game what it is. The "streamlining" isn't nearly as bad in my opinion as some gamers make it out to be, and we haven't really lost as much as we've gained as the series has evolved. I do honestly believe that each game is better than the one before it, and I highly look forward to not only DLC for Skyrim, but also The Elder Scrolls 6 as well.
Out of all of the games in the series, I hold Morrowind as my personal favorite, but that is partially due to the very strong stories in that game as well as the fact that the Dunmer are my favorite character race.
But over all I like the direction that the series is moving in with each separate installment, and I think it has a very bright future ahead of it still.