Anime so good you had to read the manga

So i know there is some anime's watchers who strictly just watch anime and never venture out if that. There are alot of anime's that are 12 episodes that are great and never get another season. For me i just go read the manga or on rare occassion mabey the light novel. Example a couple years ago high rise invasion came out on Netflix and they never finished it. Everyone seemed to be mad they didnt finished it but while everyone was arguring i had already read the entire thing up until the ending. Most people will generally never know what happens. I have two qeustions first is on topic with what i'm talking about and the other is completly off topic. First for the strictly anime watchers,what was one anime you wanted to finish so badly that you actually went to read the manga? Second off topic,for the manga/light novel readers,when the manga/light novel you've read gets an anime adaptation do you still watch all the episodes or just the first one to see if they f**ked it up? I felt like a proud dad how everyone loved solo leveling and i hear omnicient reader is getting one so can't wait.