I love the Mike Mignola Hellboy comics, and this movie is a pretty massive deviation from that source material. Oddly though, I'm kind of not bothered by that. In fact in some cases, like that of the character of Karl Ruprecht Kroenen, the film version is actually an improvement. A regular re-watch of Hellboy is a pretty frequent occurrence in my household.
Final rating:★★★★ - Very strong appeal. A personal favourite.