I don't believe that I have ever read the entirety of it, but I did buy a few issues as they came out (Back in my college days, god, how I miss them.), and I didn't really feel as strongly as other people felt, I guess. I felt that yet ANOTHER origin story for Superman was unnecessary, and I felt that this was somewhat drawn out. I did think that there was some good writing and a few touching moments and the artwork by Yu was very good, but overall, I just found the story to not be anything special, and too long. I think that Mark Waid said that this was the best thing that he wrote, and I know that this was something of a dream project for him, but I definitely don't think that this is one of the best Superman stories (It usually makes the Top 10 lists.). I don't know, maybe hardcore Superman fans (Like Waid is.) were the core audience for this one.
I wasn't very impressed on my initial reading, but subsequent reading fared much better. The biggest problem with "Birthright" is that Waid was never able to take it further than what he did, and so it remains an outlier for the most part.