Devil May Cry - 10/10 for it's time. It's still great and it's my personal favourite but now that the genre has evolved, some of the elements (first-person underwater section anyone?) are really out of place. Still has the best soundtrack of the series, or any action game for that matter.
Devil May Cry 2 - I only played it once when it was released, and I enjoyed it well enough from what I remember. But I haven't replayed it since so I can't really rate it. At the time I had only played DMC1 on easy auto mode because it was just too hard for me, so I doubt a lot of the complaints about DMC2 stood out to me.
Devil May Cry 3 - 9/10. Boss fights, weapons, and combo system were all amazing but the environments, regular enemies and music weren't that great.
Devil May Cry 4 - 9/10. Obviously an unfinished game. Rehashed levels and bosses are a let down, but for me DMC4 has the greatest gameplay of the genre in Dante, and a nice new style for the series in Nero.
Devil may Cry - 6/10 from what I've played. Lame bosses, lame colour-coded enemies, lame music, lame platforming (it's better than it was in the previous games but there's way too much of it), lame UE3, lame 30fps, etc etc. But, somewhere in there there's a great combat system, it's just hindered by the confused weapon and enemy design.