My question is what's the biggest difference between the Manga and the Novels?

 

Are the Novels just a compilation of the Mangas with a few minor additions/changes?

The novels are literal novels, sir. Not graphic novels. 

Edited September 8, 201510 yr by Kaweebo

Are the Novels just a compilation of the Mangas with a few minor additions/changes?

I think that pretty much sums it up. *EDIT* Never mind, I was thinking of something else. Kaweebo's correct, though.

Edited September 8, 201510 yr by JustinisMii

They're different. I would say the novels are more accurate to the games and don't take as many liberties as the manga, but they do still add in some interesting information and moments that aren't in either the games or the manga. 

Edited September 8, 201510 yr by soraspromise

The manga took a much lighter, comedic look at it, while the novel kept a lot of the original darkness of the game. however, a few of the villians are changed, and at least 5 worlds are fully left out, while the manga only left out 2.

Other wise, not a lot is different. The base story is the same.