The Hobbit (with 1 or 2 others) is the most anticipated film of 2012 and 2013. It follows an incredibly successful trilogy in the early 2000's and is one of the most well-loved children's books of all time.
Yes we have big-blockbuster films coming out over the same 2 years, such as the Hunger Games, but in no way is it more anticipated nor does it receive as much publicity and media attention than the Hobbit has already (and will continue) to receive.
It is based on a book far more well known and with far more books sold (i realise it has been in publication for much longer) and i think has a build in fanbase not just from the book(s) but also from the LOTR movies which loads of people love even though they havent read the books.
Also this is on a LOTR forum so although people are open minded i would say there will be still bias here towards LOTR.
Finally i think the movie will just be better as i prefer the hobbit story - one of the first stories i totally got into as a child and so holds a special place in my heart for that reason.
About the Hunger games not selling as well as certain Harry Potter movies (seven, pt two, I think), or Dark Knight; the connection between these two of course is that they both are sequels. Like you, I'm wondering how much the "sequel/prequel" aspect of TH will play into its sales. I am kind of surrounded by a huge LOTR fanbase (both on TORn, and with my friend in RL), so I sometimes have some trouble putting it into perspective, but I also have trouble believing they won't be even more successful than the LOTR movies for the same reason.
If we're seeing hundreds of ads for The Hobbit on TV in September/October, than it has good odds to make a big buck, but will it top Hunger Games? I honestly can't say. HG has the advantage of being something fresh and essentially out of the blue (from how I see it). I try not to guess these things these days.
I think it's surprisingly hard to judge. They both have a lot going for them, but from vastly different angles.
The Hunger Games does have an advantage of being something fresh and never-before seen. A lot of people had read Collins' books before the release, yes, but most of the people I knew read them a month before or the week the film came out. It had the advantage of being a "wildfire" hit: it grew lightning-fast into a trend that nearly everyone wanted to be a part of.
But a lot of the young people who are fans of The Hunger Games grew up with the LOTR film trilogy. Some (especially us college-aged kids) even went to see them when they came out. I don't know why anyone who grew up with LOTR would not want to re-visit Middle Earth through The Hobbit.
Another thing is that if I was a parent, I would be a lot more willing to take my ten-year-old to see The Hobbit than The Hunger Games. The violence of Middle Earth is far less emotionally jarring than The Hunger Games. It's free peoples battling dark, evil creatures rather than children ruthlessly killing other children. Plus, The Hobbit is much more of a literary tradition that older audiences acknowledge and enjoy. I think both of these things suggest a much broader audience for The Hobbit than The Hunger Games.
What made The Hunger Games such a success was a potent combination between excellent advertising that sold the film as the cool new thing (from People magazine specials to a soundtrack chock full of indie artists) and loyal word-out-mouth from readers. The Hobbit will not be successful for either of those two things, firstly, because Tolkien has already been established as "cool" in culture. (Albeit, not in the way THG, since it is impossible to push it into the same "pop" market for a variety of reasons: it isn't about young, attractive people, there is no romance, it doesn't involve any massive trend in pop-fiction right now like dystopian or vampires, etc.), and secondly, because so many people have already read The Hobbit, and they've been talking about it for years and years. It is not an underground book, or even a book that is kind of "sectioned off" like Hunger Games is to YA lit. The kind of out-of-nowhere phenomenon that THG is enjoying isn't going to happen because The Hobbit has existed as a cherished classic for decades.
This is kind of a messy, round-a-bout of saying that no, The Hobbit will probably not be as overwhelmingly (and suddenly) huge with young people as THG was, but... I still think it's going to be bigger. And there's going to be much more variety to the kinds of people who not only see it, but enjoy it enough to go and see it again (and again). For a lot of us, this was our childhood, whether ours parent's were reading the books to us, we were marathoning the films in middle school, or discovering the books on our own in our teens. And for some of us, it was our parents' childhood, too. There is this beautiful generational legacy to Tolkien's work which Suzanne Collins might enjoy to a certain extent, but it'll take another thirty years. While The Hunger Games may be a sensational success, Tolkien's legendarium is the yard-stick by which all other fantasy is judged, and the films have had a profound affect on an entire generation of young people over the last decade. As far as we can see, this is the only "sequel" we're going to get. I can't see why it wouldn't be just as big, if not bigger, than The Hunger Games franchise.
Because I have not and will not see Hunger Games. It has zero appeal to me. And that might be what puts The Hobbit over the edge is HG only appeals to certain demographics and TH will carry over a large audience established by LotR.