I'm rewatching season 1, the walkers act so differently. They climb, rest, act more human. As with the walkers now, they are more zombie like. I wonder if this was deliberate? The more time goes by, the more the walkers are slower, dumber.
I don't know, some of them were moving pretty fast at times. Maybe it just depends on how long they were walkers. A lot of the ones the first season were "new" yet.