"Is this the next big thing?"
No, it isn't next big thing, but it is a darn nice game with a solid online community. Particularly if you were into the books (or movies), then the quests become very interesting -- you'll actually spend time reading them and getting caught up in the lore.
The game had a remarkably solid launch, which is not exactly common in the MMORPG sphere (cf, the complete annd utter state of disaster and drama provided by Vanguard:Saga of Heros for contrast). The play is solid and the artwork lovely. Review sights have generally been very favorable, and rightly so IMO.
This is NOT the game for you if you're looking to level up as fast as possible to raid end-game conent (there really isn't much). LOTRO is much more about the journey and the lore, and so attracts folks with a different mindset than "let's raid Onyxia and ZG 500 times to get gear" [gratuitous WoW reference, sorry]. The combat is different than most FPS, and takes getting used to; initially it drove me nuts.
As a freebie, it is definately worth a look. Enjoy the opening quest lines -- it is the hook that has kept me there. You'll feel a bit on rails for the first couple of hours, which I know bothers some folks, but once you're past that your pretty much free to do what you like. Say hello to Lobilia Baggins in the Shire; she's just as nasty as you would expect ;-)