Quick thoughts on Kebab:
Great Turkish Bombard: Siege units aren't as important this game because they're vulnerable and are somewhat replaced by the Battering Ram, but I often find myself building a few; getting better siege units while also getting them faster is nice. Also, getting a full pop city is potentially amazing--this could be kind of difficult to hold onto in the short term, since large cities can kind of be troublesome, but the long-term benefits way outweigh the short term annoyance. Also, the amenity and loyalty might offset that altogether, so we'll have to see how this works in action. Right now though, this seems pretty good.
Grand Vizier: This is either going to be incredible or inconsequential. I feel like we're overlooking just how many military bonuses the Ottomans get out of this one governor: this can potentially give your units +5 combat versus other units, and a whopping +15 combat strength versus a city he's stationed in (if I'm reading this right). That's just outright disgusting. He also gives you a bonus for constructing units, which will be really helpful throughout the whole game, while also giving the Ottomans a chance for early war before all their bonuses kick in. Additionally, he's a pretty good diplomatic governor, meaning that the Ottomans are in a similar vein of Persia, in that they can play the warmonger game without facing the diplomatic consequences. Of course, upgrading Ibrahim means forgoing upgrades for Magnus, Liang, Pingala, or Reyna, which are really important to the current Civ VI meta. We'll have to see if we can afford not upgrading them in favor of Ibrahim, but this has the potential to be a really strong ability; unique regardless, so I'm all for it.
Grand Bazaar: This seems like it's dependent on the context. Built in a city with a lot of luxes, it could be incredible. Otherwise, just decent. We'll have to see how impactful the strategic resource thing is, but I imagine that's a pretty decent extra chunk, even if it's only one. Seems good, but going to need hands on experience before I definitively say how good.
Janissary: Ok, this is the one where I have no idea what to think. Taking it at face value, holy crap it's amazing. More combat strength, a free promotion, and it being much cheaper? Yes please! However, that population cost aspect it carries is a real bummer. But, given the UA and low production cost, building it in conquered cities shouldn't be a problem. And since it's a Musketman replacement, it should be able to be upgraded into from Swordsmen. We'll have to see how it fares in practice, but the potential is really high here. It comes in the late mid-game though, so the delay could hurt it.
Barbary Corsairs: Ok, so we all know how good the Jong is due to it coming so early, so depending on where exactly the Corsair is located on the tech/civics tree, this could be an amazing unit. However, it's probably not as good as the Jong since the Jong has that easy to achieve combat bonus, but it still likely will be a tyrant on the seas. The pillaging bonus is particularly interesting, especially considering how pillaging rewards scale now, making doing so more worthwhile. Again, seems promising.
Overall, I think the Ottomans are going to be really fun to play, and could potentially be quite good. However, I don't think they're going to be top-tier, since most of the bonuses don't activate until the mid-game, and a lot of the really strong ones in here you're going to have to bend over backwards. However, Grant Vizier and GTB are potentially game-breaking in some regard, so we'll have to see how the Ottomans fare in the actual release.
As of right now, I think the current PR for the GS Civs is: Maori>Hungary>Inca>Sweden>Ottomans>Canada>Mali.