Great Mangas but Disappointing Animes (and Vice-Versa)

Im just curious if you guys ran over to a manga/anime that was really well-made and then discover that there was an anime/manga adaptation so you decide to watch it,, but turns out the anime/manga was worst than you thought? (maybe not worst but changed the storyline/ending or something)
Just want to share that Pokemon anime and game is very child-friendly but the manga is kinda dark... ┗( T﹏T )┛