Overall, Berserk is somewhat polarising. The Golden Age is one of the best arcs in any manga, though every arc afterwards is a definite step down in writing quality beyond Guts constantly being developed. That's not to say any of the arcs were bad, bar the events that occured part way through the Kushan Arc and beyond, but it never came close to the same heights as before. It still has potential to retain that status though due to the possibilities it's finale holds from various points of foreshadowing thus far. There are definitely manga out there with a more consistent quality, though very few still come close to reaching Berserk's heights. I'd overall rate it as still being a high tier/lower top tier series, though it definitely needs to make improvements to stay like that.
Also, the art is God tier, with the only series I've seen matching or surpassing it being Vagabond, maybe some of Tetsuo Hara's later works too like Souten no Ken.