Re: Walkers being smart enough to open doors, as in S1: that was Morgan's wife, trying desperately to get into their home. It does seem as though S1 walkers were more adept, smarter (used in the loosest sense of the word), used actual hand-eye coordination, climbed fences, etc. My theory is that the newbie walkers of S1 had more humanity left in the synapses of their zombie-brains. At this point,, years into the Apocalypse, nothing is left except Raw Walker Instinct.
(sorry, quote function isn't working for me tonight)