For me, the title track, 'help' stands out loads as being on a higher platform than the other songs on the album- and I reckon that song alone brings the whole album up to a higher credibility (if that's a word)
I think it's hard to tell if the album is underrated because it's one thing to compare it everything that was going on in the music field at the time- like albums by other artists but it's quite another to compare it to the Beatle's other albums. I guess it comes down to personal preference and it seems that most people's personal opinions are that rubber soul, revolver and pepper were 'better'. I'm afraid I would be inclined to agree that rubber soul was 'better' in my opinion- I can't get over how modern it still sounds!
So basically I'm saying Help is more overlooked than underrated. I think it gets more a lack of praise rather than bad praise? From what I've seen anyway.
By the way, about Lennon's favourite songs which were discussed earlier in the thread, just to mention that I've read that he liked 'Across the Universe' (he described it as poetry, and a song which was written kind of 'through' him- it wasn't actually him writing it) and 'Come Together' (just read this somewhere)