It depends entirely upon your TV...
I'm still a huge CRT fan and the current Sony that I use does an incredible job with scaling images. 480i games are extremely crisp and clean now and, oftentimes, look as good as 480p titles. My previous Panasonic set did a terrible job with 480i, though, and I hated when a game lacked progressive support.
Non-CRT sets do even worse with 480i. I've used a number of different LCD, Plasma, and DLP sets of varying sizes and none of them were able to deliver a good picture for all possible resolutions. In fact, unless a game supported 720p or something, the image quality would be pretty poor. 480p games were extremely chunky looking...even on the smaller sets.
On my set, 90% of my PS2 games look extremely nice and received a rather substantial image quality boost. Ridge Racer V is actually very very clean (similar to those images captured by maskrider through Dscaler.
I see ICO being mentioned, though...
ICO runs in a much lower resolution than your standard PS2 title and does not work well on HDTVs. The Sony I use does a pretty good job, though. It is very sharp, but a bit pixelated (kinda like using an emulator on the PC with no screen filters). More commonly, though, an HDTV will lead to a very pixelated and blurry image.
What are you using Synbios459?