I bought Deadwood after hearing how good it was and didn't really enjoy it after "marathoning" the first season with my roommates. It definitely seems like a show that I need to watch an episode or two at a time and think about, rather than a show like HIMYM where I could just watch like 15 a row in a lazy day and not see a huge slip in quality like someone who watches it week to week.
you're talking about two very different types of shows. one that kills brain cells and one that is good television. I watched Deadwood in two weeks time back in 2009 and I loved it just as much as I do now going through it one episode a day. There is no correlation between a person's enjoyment of a show and how they watch it. It's ridiculous to think that. I'm sure there are many things that factored into your not being able to enjoy Deadwood. Not the least of which being that you don't have very good taste