Would have been nice for Vergil to have more stuff, but I think he's cool, I have played the game for weeks with him, and still playing in order to get more S and SS ranks.
He certainly is not slow. You can destroy a crowd of enemies with the Sparda sword, really quickly. If you lock on with R1, then go crazy slashing them with his standard combo, uppercut and stinger, then press O to teleport to the next enemy, you can totally mash them! Way quicker than most things that Dante can do. Of course you can also fire off the summoned swords at the same time, which speeds up everything he does.
His Beowulf attacks are the same speed as Dante's basically. Most of the Yamato attacks are quite slow, although the first two hits of his standard combo are quick, and his mid air slashes are quick, so you do have options even with the Yamato. But that's the whole point, that he has variety in his attacks:
Yamato is fairly slow and has really long range
Beowulf is really powerful, but slow and poor range
Sparda sword is very quick, but less damage, and average range
I think it's good that Vergil plays so differently to Dante, because it makes you play the game in another way, so it's more interesting. It gives Vergil his own personality whilst you play it. Still, yes, he should have 5 styles, and should have more weapons, and more moves, to make him even more varied.