Don't think she is that strong. At least based on how much I've seen and played her. Actually, there is simply not enough time to evaluate her, so please don't start on this)
Vault Breaker is a "gap closer" that works better as initiation than chasing/running ability since it slows you down and must be charged. W deals physical damage. Like those top lane bruisers aren't having tons of armor by the time that starts to matter. Additional effects are pretty overwhelming though. Get it once to make it better. Still, it deals the easiest damage type to counter.E has what I thought to be the most epic scaling of all, until I noticed that base damage is so small. It is powerful, though I feel that this is her way of keeping up a bit of damage if going a full-tank since she has beautiful initializing skills. And we know you aren't going to build Vi as a glass cannon. Assault and Battery is epic. I wish she made the hit while enemy is still in the air, but it doesn't matter. Yes, she can't be CC, but that is her only real gap closer. She can't stick to you by other means, unless you are already slowed by a separate effect.
Overall, I love her to bits. The style, the voice, that kit.She doesn't have the "complete OP" feeling about her, unlike our local favorite, absolute winner of all votes and Mr. Dat-ult, Sir Darius. If anything, she feels Jax - burst and sustained damage together, pretty weak early, but a nightmare to face late game.