Sure, the upcoming God of War Collection is a lot more resolution-y than the original PS2 games, but does that produce a noticeably better-looking game? Bitmob tested the original God of War games on their backwards-compatible PS3 systems and took comparison shots of both. It's clear that the Blu-ray remastering is better than the PS2 original, even with the PS3 upscaler turned on.
It certainly helps that the original source material was so good. Looking back at the first game has us impressed -- we'd forgotten how much muscle the last generation could flex.
Source - Graphics Comparison (part one) God of War 1 vs. God of War Compilation
Source - Graphics Comparison (part two) God of War 2 vs. God of War Compilation