
I think it primarily comes down to expectation for both of the trilogies. When the LOTR was announced a lot of people didn't think it could be done and Peter Jackson at this point wasn't a globally established director so people weren't expecting the films to have the success they did. The Hobbit however had the complete contrast. The Hobbit had ridiculous amounts of expectation hanging over it whether it could be helped or not so that's why it probably didn't seem as good as we'd hoped because we expected too much, me included. However there are some other significant factors specifically that make LOTR so much better than The Hobbit, commercial success and expectation aside.
One comparison generally that I find really important is the contrast of look from LOTR and The Hobbit. One reason I love LOTR is the gritty realistic feel it has to it and you can really sense New Zealand in the shots and can tell its real. However in The Hobbit everything has a glow to it and sometimes you can't tell where New Zealand ends and CGI begins.It's really obvious when something is on location however so when there is CGI environments they just don't hold up. The loss of the realism surprised me when I went to see the first Hobbit but a let it slide due to excitement.
I think something a lot of people have been talking about is the presence of comedy within The Hobbit and how everything seems to take on some form of joke or gag. For example in the final Hobbit film, Billy Connolly's character headbutts people and makes an attempt at a humorous speech towards the elves which wouldn't have been present in LOTR. The comedy in LOTR is much more subtle and when there's jokes it feels like something those characters would say in that situation with whatever scenario. In LOTR everyone is serious in war and everyone fights properly without the addition of gags. The best example of LOTR humor would be when Legolas says to Gimli at Helms Deep "Would you like me to describe it to you, or would you like me to find you a box?", this a perfect example of how the humor should have been done.
Another hot topic of conversation would be the fact that LOTR was a trilogy of films and books so it made sense. But The Hobbit was split into three films from one book and still had plot holes and added characters and parts. It annoyed me that they put in Legolas even though he isn't in the book, I haven't read the book but that's what I hear. I'm not that desperate to see old characters revived, I'd rather learn about new characters in the Middle Earth world.
I think I could spend this whole paragraph simply talking about the battle in the third film and its chaotic feel. There was so much convenience, pointless comedy and bits that just made you say "For God Sake!". Anyone who's seen the film would agree that when the Yak/Goat things came in we all were like "Where did they come from and how can they climb cliffs that steep?". I could keep up with who was fighting for who but I have to admit it was all over the place. LOTR was so simple, Orcs attack a city of men, what more do you want. We waited two films for a war and thats what we got. Legolas defying gravity on rocks.
Finally I think I should address the endings of LOTR and The Hobbit. A lot of people say that LOTR has too many endings, one person being Jack Nicholson but at least it ties up all the endings happily (Makes me shed a tear). The Hobbit ending however was just not satisfying for a 2 hr 30 min movie. I wanted to see what happened to the dwarves, Thranduil and others.
Overall I The Hobbit for the reasons above just isn't as good as LOTR, I wonder if Guillermo Del Toro directed it he would have made it better but I suppose they all had a shared vision and he co-wrote it. I think I always knew it would never be as good as LOTR but I'm just disappointed that Peter Jackson didn't give Middle Earth the same tone as before, you know, the one that won 11 Oscars.
