One of the most iconic movies of the Sixties, to be sure, but not one that has aged particularly gracefully. The main problem is that Hoffman's character steadily evolves into a creepy stalker as the film progresses. The best thing about the film besides its dead-on portrayal of the stifling awfulness of suburbia, are Robert Surtee's camera work and Sam O'Steen's editing, which still stand out as innovative.
Wes Anderson owes his style to this film, with its long dialogue-free takes overlaid with Simon & Garfunkel tracks (especially "April Come She Will").
Apologies for low quality of caps - the 1999 DVD is not a great transfer, as I unfortunately found out!