Nah, you should watch the whole series to completely understands what's going on.. But that's one fucked up, twisted plot I have ever seen. It got me hooked, like I saw the anime which was released years ago and not even the movies which had better art style. Later, I saw the movies as well which had an extra 20 mins which the 25-ep anime series didn't have. I wanted more of it.. more gore, more violence.. Then came berserk 2016, 2017. Saw 2016 and the art sucked. But oh well, the story was okay after the prequel.. Gotta see 2017.
Btw, I didnt know ya didnt watch BNHA S2 and S3. The story is just so organized and put in a fantastic way. Like, we don't see many animes where side characters gets a lotta screen time or a good character development except very very few animes. BNHA has done that. Attack On Titan on the other hand is a mind blowing action anime and the suspense is like dang. It just gets ya hooked once ya are into the show. In the first episode itself, they'll show the loss of human kind and eren's mum would be one as well. LIKE that happened in 1st episode, right off. And then the plot progresses with losses and they introduce some badass characters too. Art style is amazing. What else is needed to get fans or people in general to get hooked?
I also recommend "bungou stray dogs". This is also a dope anime. Binge watched it within a day. Has a movie coming around this year.