Maybe you missed the memo. The end isn't THE end.

The anime was only made to promote the manga. The first 3 volumes of the manga isn't even in the anime and neither are the 30 ish other volumes that are after the anime. The anime is focused on showing how and why Guts became the guy he is. The anime is also censured in a lot of places that for those who haven't read the manga just won't understand. Like how Guts was sold by Gambino and raped by a man in his youth.

The fact that Miura kills off everyone you have come to know and love (or hate) like pipin, corkus or knife-thrower whose name has slipped my mind is brilliant. It feels so meaningless and so powerful because you've spent the whole anime building a relationship with these characters. And Guts at the end having to watch Griffith rape Caska, so much anger, so much hatred, pain and sorrow gathered all at the same place, betrayel from the one man they all loved in the most profound and horrendous way. Pure genius!