From the 2 good PlayBook reviews I read, both reviewers complained about the lack of apps in the market (uh.....no kidding. It's too new at the mo), and the lack of the very basic calendar and email apps (what was RIM thinking?). Occasionally, the text was sometimes a bit too small unless you pinched to zoom, and the battery life is 7 hours.
What they didn't complain about was the UI. All the right ideas are there, notifications are great, multitasking was Ok, the browser could play flash well enough, the browser was good, and the screen was nice.
If your primary uses for ANY tablet is to browse the net, watch movies when on an airplane/train/bus/etc, and reading some PDFs or eBooks, it doesn't sound like the PlayBook is a bad choice. Actually, it seems like a GOOD choice.

For those who have very basic needs like internet and movies, I'd rather browse on a browser that can view flash pages.
I don't want a tablet, so I don't really care that much, but the PlayBook seems to be getting some negative reviews because reviewers feel that "power users" would find it lacking, and yet the iPad's UI lacks features that EVERYONE would find useful and still gets a positive review.

It lacks features that should have been added by now. It's not like iOS is new.