By the second season Sesame really hit its stride and was running on all cylinders, but even with a few faults and missteps, the first season made some great strides, and nothing to really condemn it.
To be fair, the first season of a TV show is rarely all that put together. Sesame Street is no exception, as the experimental nature of the program was in its earliest stages. It certainly wasn't bad, but there's a lot to the show that got better and better as it went on. I feel the show perfected itself late 70's up through the 80's, but you could see mark improvement as early as the second season. A more rounded Muppet character cast, more time devoted on the street to vignettes rather than teaching segments, and less reliance on repeating the same segments within an episode among other things.
Even the Muppets started to evolve. Other than the better designed green Oscar and Big Bird being an inquisitive little boy instead of a Bullwinkle wanna be, I really think the Ernie and Bert segments got better when Bert's stick in the Mud attitude was exaggerated to Jon Arbuckle levels.