I've no problem with backstory and history, so long as it's pertinent to character in the context of the story. For example, if Joe is the best forensic expert in the state, it doesn't help to say something like "...and it was because his mother made him eat Tuna on white when he was a kid". It just doesn't matter. So there ARE rules to be adhered to in literature, whether we want to obey them or not. If a writer wanders too much he/she leaves themselves open to some criticism regardless of who they are.
Tolkien drew a lot of inspiration from The Kalevala and many epics: true. Do they necessarily make for good reading just because they're "epic"? No.
The problem with literary criticism is that it is very subjective. There's no hard and fast set of rules that say this must happen, but there is I think concensus on certain fundamentals, ie: Introduction - Rising Action - Complication - Resolution - Denoument. It's fair to say that Tolkien followed this, it's just that the stuff in-between is what bothers me personally (on occasion).