I have the original PS2 and it's played every film I've chucked at it. Which isn't that much I admit (lots of other DVD players in the house). But most films are dual layer. You can tell when they pause for a split second that it is changing layer.
But some DVDs don't play in some systems. My main DVD player, for example, is more likely to skip on a lightly scratched DVD than my DVD recorder. But the image from the recorder is worse. Typical. My worst example was Troy from Blockbusters, which completely failed in my main DVD player, but played fine in the PS2 and the DVD recorder. Annoyingly my main DVD player is the only one with Dolby Digital completely setup (is part of the Hi-fi).
Cheers
I am 99% probably lying in bed right now... so don't blame me for crappy typing