I'll certainly second that.
I've read the Hobbit, the trilogy and the Silmarillion and enjoyed them all, though the three are very different from each other. The Silmarillion reads very much like a History book and unless you've got an amazing capacity to remember names, things will start to blur. Cool stuff to know though is that there ARE a few characters from the Silmarillion that are still alive in the others. (Elves of course)
But yeah, it's mostly just the background history for the trilogy, not a story in and of itself.
As far as Moria>Mordor, keep in mind that until Sauron has the ring he's pretty much stuck as an incoporeal entity.
If you want to get technical, he's technically a Maiar (can't remember spelling) just like a Balrog is, though he's much more advanced in many ways. Balrogs were made by Sauron's boss (in the Silmarillion) to serve as a military force in the battles that were fought in the old world.
So, technically Sauron is greater than a Balrog, but in the trilogy he is massively weakened by the lack of the ring. (Think of the ring like a Lich's phlactry)
I enjoyed the movies. Thought they were great cinematography (if a bit long). But, honestly, there was no way they could include everything in the books. My biggest pet peeve? In the cave near Osgiliath when Faramir has Sam and Frodo and Gollum and he says 'The ring shall go to Gondor'. And then takes them to Osgiliath where they engage in a fight and Frodo, et. al. run... Totally never happened.
In the books Faramir was deliberately intended to reflect the honor of the Steward line, while Boromir gave into the temptation of the ring. The movies cheapened his character drastically with that line.
(Can you tell I like LOTR?)