Just saw the second part of the trilogy and these are my thoughts so far.
Firstly, it's been a really long time since I read LotR and even a longer time since I read The Hobbit, so my memory of them might be a bit foggy. I've also never read Silmarillion or The Book of Unfinished tales. I feel that The Hobbit (book) was what I want to call "silly" fantasy adventure what with it's trolls turning into stone at sunlight etc. LotR was at the beginning also a "silly" fantasy adventure, but it had this shadow looming in the background from the beginning and as the book progressed, it grew bigger and bigger until finally the book became "serious" fantasy adventure. Let me state here, that I enjoy "silly" fantasy adventure way more, and my favorite part of LotR was the beginning, as in everything happening before the hobbits reach Bree.
LotR movies pretty much ditched the entire "silliness" from the beginning except in the battle scenes, and to me it felt that the whole movie trilogy was trying to be the most epic and serious thing ever with the fight scenes stuck in between as kind of relief to help the audience bear it. The Hobbit however I find strikes pretty good balance with serious vs. silly and some of the additions I really like. I agree there was way too much fighting, the whole orcs are chasing us-plotline is stupid, as is the romance subplot. While the necromancer didn't appear in the original book I felt it was a good addition. One scene I really liked in the first Hobbit movie, was the meeting with Gandalf, Galadriel and Saruman. In general I feel that the Hobbit movies portrayed "the good" side way better. LotR movies were about a fight between good and evil, and whereas evil might fight among each other, the good will always stand united. The Hobbit movies show how a big chunk of decisions made by "good" characters are dictated by pride, greed or sheer stupidity. The Lake-town for example showed that living in the lands of "good" isn't happy or peaceful. They are suffering when the nobility are living a glamorous life. I also especially liked the elven king who would just choose to protect his own lands and let's the rest of the world fall in ruin.
TL; DR: It's way too incoherent to be summarized. I don't know what I wanted to say myself.