This is by far my favorite anime. It is very bloody and violent, so I do not recommend it for anyone who does not wish to see those things, but if you don't mind, then it is amazing.
It follows a young man named "Guts" through his life. Guts is an interesting character in the fact that he runs towards death in battle headfirst, but also that he always wields a sword that is supposed to be too large for a person with his frame. He always has the largest weapon on the battlefield. There are many plot twists that are interesting, but I will not get into them because I do not want to give any spoilers.
I will say that there are two versions- one has 25 episodes that are each around 20 minutes and another is longer, movie-like episodes. I have seen both and the 25 episode version is MUCH better in my opinion. I would recommend not watching any version except the 25 episode version made in 1997