Besides the basic ability to actually play these games on a current system, the other benefit to the God of War Collection is the visual upgrade the game undertook. Basically, all of the in-game textures have been cleaned up to be bigger and crisper, meanwhile the game itself now outputs at 720p and claims to hit a steady 60 frames per second (as opposed to getting to that point occasionally). What this means is, simply put, the game looks a lot better now. While I was stunned to see how well God of War and God of War II looked in HD, it still doesn't look as good as other PS3 games... but that is completely understandable. It isn't like the developers completely redid the character models and levels; for the most part, the game just got a presentation upgrade.
Still, I wanted to know what the value was to gamers who already owned the original titles for the PS2. Being lucky enough to have a PS3 that can actually play old PS2 games, I popped in the old GoW games and fiddled with the various graphical settings both in the game and on the PS3 for playing PS2 games. These settings include the game's own widescreen, progressive scan and soften values, as well as the PS3's own Full Screen/Normal selection and Smoothing settings. Like I said, I played around with the various settings, trying different combinations, and while the PS3 version of God of War always looked substantially better than the PS2 one, God of War II never really differed that much across the platforms (at least not when I had all the settings bumped up on the PS2 version). This makes sense though since God of War II was released after the PS3 came out and probably with the intention of PS3 owners being able to play the game on the new system (before that functionality was taken away, of course), so naturally the developers would have done whatever they could at the time to make the game look its best on both platforms.
What is noticeable in both games, though moreso in the earlier title, is the fact that, while the in-game graphics got an upgrade, the cinematics didn't. At the time of both games' original releases, care was taken so that the pre-rendered videos matched the in-game graphics as much as possible in order to keep the transitions between the two from being too jarring. With the upgrade in in-game visuals though, the striking nature is all to apparent. Funnily enough however, while the developers were trying to make the bump up in graphics during cinematics not be too drastic, now the fall in visual quality during those cut-scenes is visible. As for the visual side, these jarring changes between in-game and pre-rendered visuals is the only downside, especially if you either don't have the old PS2 games already, or have them but not a PS3 that can upscale them.