One thing I've noticed running games in the new WoD is that it's a pain to track Defense and Armor. Players and GMs often forget to deduct it, resulting in more hits and more damage, which is annoying when villains and mooks go down easy, but terrible when PCs die too fast. Remembering and re-rolling happens a lot - but only if the remembering happens within a few seconds. By the time the next combatant gets his or her action, it's too late.
What's more, some players (one I know, at least) dislike the new Storytelling system for taking the defense roll away from players. I personally prefer rolling dice as little as possible, but I can see why some players like taking luck in their own hands.
A modification for this is to roll defense and armor and subtract the successes from the attacker's successes instead of subtracting it directly from the attacker's dice pool. Statistically, I believe it works out the same except for some decreased variance (more dice = less variance).
An additional advantage is that this keeps the attacker (if it's a PC) from knowing the defense traits of the defender. In the normal system, the attacking player says "my character has 7 dice to hit the bad guy" and the GM says "subtract 4" letting the player know that the 'bad guy' has a total defense plus armor of 4. If the GM just rolls, he can keep it secret from the player. The player still learns how many successes are subtracted, but with the reroll of 10s, it's hard to tell how many dice were rolled.
The flaw is that you lose the relative simplicity of one roll per action, and the GM and players have to do stuff on other people's actions other than observe and make notes.
Thoughts from those of you who've played the system?