She's back! It seems that Riot is simply not content to let Camille sit outside the spotlight for all that long, and the latest round of buffs to the champion certainly managed to get her noticed again, especially in competitive play. Camille was already seeing limited play in the competitive scene before Patch 7.12, most notably by Samsung Galaxy's CuVee, but ever since that patch hit her play rate has absolutely exploded.
So why is Camille so good? Easy. She only has one true counter, Fiora, and she's altogether excellent against many of the best champions in the top lane right now, especially since Kennen is often banned or ignored anyways these days. She's still excellent against Shen and Gragas, both of whom remain common picks, and she outright dominates the latest big top lane pick, Jarvan IV. Jarvan's entire damage combo is dodgeable by a skilled Camille, as activating Hextech Ultimatum provides her with invulnerability frames. Anyone who's played Jarvan is already painfully aware of how vulnerable he is while his damage combo is on cooldown, so being locked in the Hextech Ultimatum is pretty much the last place he wants to be while he waits for Dragon Strike to come back off cooldown.
So how do you build Camille and play her? Well, if you remember how she played the last time she was popular then you know how to play her now. She still relies on the old Tiamet>Trinity Force>Titanic Hydra combination of items, though if you plan to commit hard to the splitpush plan you might want to consider the Ravenous Hydra instead. After that, it's just whatever tank items suit your fancy, as Camille doesn't really need any more damage to blow the face off any squishy target she gets on top of.
In terms of playstyle, Camille's a hard one to pin down. She's effective in both the split push and in teamfighting, so it will take a bit of experience to figure out which one you should be focusing on. If your team can follow up on the Hextech Ultimatum with, say, something like a Command: Shockwave, then you probably want to group up with your team. If your team is instead full of squishy backliners without much offensive presence, you probably should keep yourself in the side lane.
As long as you can dodge her most potent counters -- both Fiora and Tryndamere are hopeless matchups -- then now is the time to get back into playing Camille. She's a strong carry top laner with a kit that lesser champions simply drool over. If you like mobility, tons of burst damage, and oneo f the most oppressive ultimates in the game, then you're going to love Camille.