Here's my opinion =
DMC2 was a good action game, but a lacking DMC title.
Story - The story was ok in my eyes, if not a little simple. The biggest problem in my eyes was Arius - he wasn't a very likeable bad guy. He wasn't scary or cool, and fighting him wasn't satisfying (he just sat there, shot, teleported occasionally and relied more on lackeys). Also, Dante had less personal involvement to the mission in comparison to 1 and 3, which made it less emotionally involving.
Gameplay - On the plus side, there were some good points - the new abilities to wall run, shoot downward in midair and various dodging moves were really nice, and even went towards DMC (mainly the trickster style). However, the combat wasnt as satisfying - combos felt slow and simple (and Dante's stinger was more of a 'flopper'). Guns were way overpowered, so the balance in weaponry really tipped the scales in favour of gunplay, making swords fairly redundant. The game was far too easy, and the added Desperation Devil Trigger made it even easier. Even DMD! difficulty wasnt that challenging.
Dante - Dante looked awesome, and he was cool. Yes I can even say I liked him, but he wasn't the Dante we'd grown to love in DMC1. I say great design in his appearance, but a bad move on the personality.
Lucia - Great, in my opinion. A whole extra character with her own weapons, storyline and some variation on missions. Very nice, and a great addition to replay value. She looked pretty nice, too
Weapons:
Pros - Rebellion introduced to the series, the addition of submachine guns, and a choice of swords (I liked them all). Ability to upgrade the power of swords so that later you feel Dante is stronger.
Cons - No real variation, all swords were basically the same except for different damage/range values. No other weapons, i.e. gauntlets, which was a step back from DMC1. Also, no abilities to learn.
Enemies - Average enemies at best, and they seemed an odd selection with no real theme. Disappointing really. Bolverk was cool, but not as good as Nelo Angelo was. Dante's last boss was cool. The rest weren't really very good in my opinion, and lacked the personality that DMC1's bosses had displayed. Phantom was easy compared to his DMC1 counterpart, but it was nice to see an old enemy.
So basically I think it was a good action game, with a good few new concepts that I like, but they failed to keep up with DMC1's standards in a lot of areas. Don't get me wrong, I like the game - but the others were better.