Well, the second one is probably like ten times better. I've read a lot of reviews about it. It doesn't really center on what happened on the movie (like BFME 1 does), but is actually about the war against mordor in other parts of Middle Earth. But I did read that you can fight any of the battles from BFME 1 & 2 in the second one, plus there's this little hero creator thing, where you get to create your own heroes and customize how they look and what abilities they have, etc.
So I guess I'd recommend just getting the second one, cuz it's like the first one times ten, lol... or, so I've heard.