Visually, Quinn is fairly impressive. Colorful, but muted. Her animations are smooth and her attacks are clear. Skills are extremely noticeable (as is her passive) - no visibility issues at all.

Kit Harrier (passive) is basically a free Sunlight proc every 6 seconds, and on-demand with E. Getting hit by a Mark>AA>E>AA>Q combo is a surprising amount of burst and almost completely unavoidable (though if you have fast enough reflexes, Quinn is not untargetable while she E's, and Q is a skillshot you can avoid).

The combo of Mark>Q>AA>E>AA is also strong, offers 2 Harrier procs, and the blind on Q makes it hard to retaliate (which I guess is understandable - if it's harder to initiate, it should be more rewarding).

Quinn's ult is an amazing kill move, and Valor's AS and MS buffs make him even more bursty than Quinn. They do share a health pool, though, and Valor is melee only.

Expected Lane Synergy Quinn can play safe, but I feel like a kill lane is right up her alley. A Leona support basically doubles the amount of procs you get in a combo, and the CC lockdown will probably guarantee a kill. Go with Janna for double bird synergy, there might even be a hidden passive there.

Overall I'm not much of an ADC player, but Quinn is really fun to play and I feel like if I want to master any ADC, it should be her.