Overall, Fiora is a somewhat balanced somewhat broken champion. I'll explain.

Her passive overall is useless. You regenerate 8 health at level 1 OVER 6 seconds. That's the significant part It takes so long to receive the full amount, late game, your fights last maybe 5 seconds, regenerate 100 health over the course of the fight. The health regeneration for a hit is lower than her base hp regen. If you attack an enemy champion, you are bound to take damage, therefore the stacked regeneration is also useless You may only regenerate health equal to half the damage of 1 attack, after taking 5 hits? Complaints about this passive helping her laning phase are ludacris. If her passive would regenerate a percentage of her maximum health, that would allow her passive to really have some use. Even if it's 3/4/5% over 6 seconds, it would allow her passive to become a tad bit useful. Stacking up to 3 times. (Con)

Lunge scales fairly lowly with damage, so it's a gap closing ability. You can engage with it, but you cannot use the dash to quick engage and escape even with 4 seconds. It's an alright ability which allows you to catch up to enemies. This should become a skillshot, having the second lunge active if you land the first one. (Neither)

Riposte is a beast. (Pro)

Burst of speed is also fine. The speed boost is nice, but there SHOULD be a small movement speed buff implemented without needing to land auto attacks. A 10% movement speed buff for 3 seconds without stacking would give her a little utility, and it would make it more of a fair ability. (Neither)

Omnislash, relatively strong ability. Should apply lifesteal only. Not abilities like Black Cleaver etc.

Fiora has 0 cc. 0 escape.. Generally, she's a champion who needs some utility. But her offense is very good. If her lunge was made a skill shot, or if she was to have some sort of utility, she'd be a more balanced champion. People continually say this champion is overpowered but, in all games 75+ % of all Fiora's fail hard, even when they play well. Even Sejuani players did better with Sejuani. Who isn't even considered OP. This is just my observation from 10 hours of gameplay.

I've tried to be as fair as possible.