§pectre: Berserk was on my to watch list. What makes it good?
I'll talk about manga, but it goes for anime too. First thing you should know is that it is extremely graphic. Berserk takes place in dark, vile, twisted, sadistic world. There is no taboo topic here, everything is presented without censure. I don't think there is some other work (of any form of art) that has become as mainstream while being this brutal. Although, it is toned down in the anime (the one from the 90's and movie trilogy, haven't seen the new series).
Now, what makes it great? Are there epic battles to rise your adrenaline. Yes. Is there world full of mysteries waiting to be uncovered? Yes. Are there creatively designed monsters? Yes. But all that can be found in other works of fantasy (not as nicely drawn). What makes Berserk truly amazing is how it treats human characters. It dives deep into human relationships, emotions, fears, weaknesses. They feel real. And they don't shape this fucked up world they live in, it shapes them. It breaks them physically, mentally and emotionally, and we can relate, we can understand them. That is where this story shines.
And yeah, somebody is going to say "That main guy wields a huge sword and fights monsters with it, how is that real?". Well, although there is an explanation, you will have to give it a benefit of the doubt when it comes to the sword. But he is just a human, he gets hurt and bleeds.
Everything that goes on for this long will have some oscillations in quality, and Berserk is no exception. But if you start reading it and you do like it, you will go all the way.