The first two seasons of the anime follow the manga almost exactly, which is seemingly rare.
The first season doesn't really have an overall arc to it, but takes it's time with character development. This is a good thing, especially given how deep some of the characters are. It also has a fair amount of humor, and is very entertaining.
The second season starts the real story, and quickly picks up the pace. We learn more about Kenshin's past, there are some awesome battles, still great character development. By the end, the viewer is still left wondering about kenshin's past, and there are still plenty of open questions. I thought the third season would finally reveal all-- and I was vastly disappointed.
The only reason I don't give Kenshin a 10 is because of the third season. It basically tosses away a lot of the developments and fills the story with fillers and really pointless arcs. The final arc in the manga answered all the remaining questions, had an actual story, and was overall captivating.
But for whatever reason the anime ignored all of it. So if I were you, I would only watch the first two seasons, and then read the final arc of the manga. (There are two OVA's that act as a prequel and then a sequel, but these fall short of the manga too. The animation changes in a bad way, the tone is much different, and the sequel changes a lot of Kenshin's character. The first OVA is good, but the manga is better).
