Many clips have been added over the first few months that it's been online. Sesame Workshop plans on including more soon.
I would like for more first seaosn clips to be included, though what is there is great. There are a lot of rare ones that I've heard of (thanks to the CTW Archives having papers listing nearly every first season sketch and those papers being scanned on Muppet Wiki) but haven't seen.
It seems like many of the recurring film and animation segmnets have only a handful of segments included so far. There's only one baker, jazz numbers, Typewriter, and detective series segment, two Mad Painter and Pinball Number Count segments, and no Teeny Little Superguy, letter candles, speech balloon, or Alice Braitwaite Goodyshoes segments. I forget how many bellhop cartoons there are.
There are a lot of rarities that I hope get put up soon, including Lefty's attempt to sell Ernie a letter U, One Song (Song of One), There's a Hole in the Bucket, Lucy in the Sky with Diamonds, The Count on Miami Mice (heck, I'd like for any Miami Mice segment to be included) and at Grover's resturaunt, and others. I'd also like for the site to include segmnets with Professor Hastings.
I wonder if Sesame Workshop has to negotiate residuals for these clips, despite them being free. I haven't seen any segments with copyrighted outside characters (except Kermit), very few clips with celebrity guest stars, and none of the first season song covers.