What is better - graphics wise, gameplay wise, replay wise?
It's such a tough call considering they're both among the best of the gen and probably in my top 3 with Soulcalibur if I had to pick my faves. And they're different enough to make it hard to match them against eachother.
Graphics wise: Tough call. They're both the best looking games I've played. If I had to break it down, I'd say during gameplay, RE4, but MGS3's graphics really shine during the cutsenes and it betters RE4's.
Game play: Depends on what you're looking for. MGS3 can be played various ways. You can rely on the stealth, you can run in guns blazing, or you can even use hand to hand combat for most of it. No matter what you do though, you will be spending a bit of time hiding in grass. RE4 is for the most part, a non-stop slaughter fest. So, experimentally and variety wise, MGS3 wins, for pure action, RE4. MGS3 also has the superior boss fights.
Repay wise: Again, depends on what you're looking for. MGS3 has more secrets and little hidden things that you're likely to miss your first time, so there's a lot of reasons to go back and play again, but the game experience doesn't really change much unless you decide to change it and set rules for yourself using different/less weapons, no kills, etc). RE4's fast action emphasis and slightly shorter game makes it a friendlier for replays as well as unlockable weapons and other various good things you get from finishing the game and replaying, which I won't spoil.
You didn't ask, but:
Sound wise: MGS3, hands down. Excellent music and soundeffects. I'd say RE4's voice acting is a little better, as the MGS series seems to get worse with every game, but they're both really good by videogame standards (that don't use big name Hollywood talent).
Story wise: MGS3 again, no contest. RE4 probably has the weakest story of the series so far (not counting RE3 or RE0 since I never finished those). I like the characters and all, but the story wasn't as fleshedout or as interesting as say, RE2.
