YMMV, but I think there is HUGE variance in TED. The speakers who come across as the most slick/polished/used-car-salesmen types tend to stick to your mind as being representative because they are the most on-brand (i.e. they enunciate clearly, present an affect that matches that of the setting, play to the crowd, simplify their message), but there are plenty of off-brand speakers as well who do very good talks. The packaging and the contents are (thankfully) not entirely in harmony. That's TED's saving grace.

That said, some of the criticism of TED is probably justified. Evgeny Morozov, himself a former TED speaker, probably has the most cogent criticism that I've seen:

The Naked and the TED

Nassim Nicholas Taleb (author) is another prominent former speaker who is now critical of the event. He calls it "intellectually dishonest."

I haven't yet made up my mind about how to read TED culturally. I've swung back and forth between being critical and appreciative. Every time I see a crappy TED talk, I get critical. Every time I see another of the occasional good ones, I decide the thing is worthwhile.

I don't know whether it is fair to attempt a summary assessment of TED yet. It is part of a broader movement sweeping education and intellectual culture: high culture is sliding downmarket basically, while acquiring a palliative gloss that helps people ignore the gradual hollowing out of deeper intellectual traditions. I don't know yet whether that's a good thing or bad thing. I am not an unreserved fan of either high culture or low culture. Both have their problems. So a shift in the balance of power between them is complex to interpret.