Can you briefly describe each character's strength?
Well let's see.
I'd say Nero is the most balanced. None of his moves are too powerful or too weak. He's got great offense and damage output and good defense, with lots of evasive moves.
Vergil is the one I like playing the most cause he's my favorite character in the series. I'd say he excels at offense. His damage output can be insane since he can spam his Summoned Swords while he's performing combos, and with the Concentration meter at max level you can totally wreck havoc.
However he's not great at defending himself. Sure you got i-frames teleports but they're less reliable than their DMC3 version cause, just like DmC, he has to stick an SS to an enemy before he can teleport. Also teleporting back is locked to Devil Trigger mode. I'd say he's the glass cannon of the bunch.
Lady, as you can imagine, excels at ranged combat and crowd control at a distance. She struggles up close UNLESS you stick out that shotgun. At point blank, that thing destroys everything, and if you're good at jump canceling the shots, you shouldn't worry about anything.
Trish is probably THE go to character for crowd control. So many of her moves are designed to hit multiple enemies at once. Use your hand to hand moves, those are your heavy hitters, forget Sparda when you're surrounded.
And then the best for last. Dante is simply the ****ing boss. He's great at almost everything. He's got amazing offense, amazing defense, the most adaptability. Probably the only thing he lacks is good crowd control. The drawback is that he requires quite a lot of skill to be that good cause you need to be able to quick switch between weapons and Styles depending on the situation. And when I say quick, I REALLY mean it. The reward is so sweet though, DMC4 Dante is no doubt the most SSStylish character in the franchise, the cool looking stuff you can pull off with him is unparalleled.