For the most part it's a better experience, although the higher frame rate kinda breaks SotC physics from time to time, where Wander has a bit too much reaction to the colossi movements. It's easier to beat the time attacks in the PS2 version of SotC but they are not impossible in the PS3 version, just more frustrating than they needed to be. The only difference is that the ending cutscene has a squirrel in the foreground, this squirrel was removed from the American version for... some reason. I dunno.
ICO is amazing in the HD port, and they brought over the content that was missing in the American release. It's not as visually stunning as SotC but it's still nice in HD.
The disc also comes with some bonus features which are basically behind-the-scenes videos.