Story for me, but gameplay has to be at least average or fun. don't really care about graphics, the only game that I stopped playing because of bad graphics was FFVII. I didn't have a PSX at the time so I tried play it a couple of years ago but man, that game has aged horribly. Still was able to play FFVIII though.
DMC3 is the best of the series and it's not even close. if you play it the right way (trying to do combos with different devil arms, guns and styles and not just mashing buttons) you'll have a ton of fun. and the cutscenes are the best that I've seen in a video game so far (but I'm a DMC fanboy lol)