This book is full of things that need FAQs, and I really wonder about the design choices they made on some things.
Thunderer's mortar is 12" range? Wasn't it 36" before? It seems like this unit is honestly just best taken with rifles and slapped inside a skyvessel.
Thundrik gives re-rolls on hit rolls, instead of wound rolls, despite the ability having the same name and flavour text?
Can you bring an endless spell from another faction?
Can arkanaut company inside an Iron Sky Attack Squadron charge if the frigate ran?
Can garrisoned units shoot after a run?
Can we set up units inside of a skyvessel during deployment?
I also hate that the skyvessels have a 10 and 15 model limit basically. It seems like it's beneficial to take an understrength unit of 14 thunderers (or 9 company) so you can fit a hero in there with them. The penalty is too binary, either you're perfectly fine, or your skyvessel is completely crippled.
The good:
I think the Iron Sky Attack Squadron has a lot of potential. Your frigates can fly high and unload 10 dudes on an objective turn 1. It also solves the problem of arkanaut company having 9" range, since they can disembark within 6" of the skyvessel, so potentially only 3" away from an enemy (and charge 3d6). At a flat 800pts for the minimum, taking this seems great. Then your frigate can just blast stuff while your garbage units screen for it.
I think Ironclads are really good too, I just wish they allowed you to have 16 models instead of 15 without penalty. The price of 510 is definitely on purpose, because those 10pts lock you out of a lot of options I would like to have. The Volley Cannon does the most damage, but only has a 18" range. Works out pretty well with thunderers 18" range. Alternatively, the sky cannon is nice with the option for more range, or less range and more damage. The flat 6 damage looks nice, but at one shot it's not as good as the others. 10 thunderers + admiral + navigator seems like a good garrison for it.
The new hero is really good. Unlocks balloon battleline and does massive damage. Getting a flat 3 heal (or even 4 with trait I think) is pretty nice, especially since it happens in the hero phase and ships don't want to be at 7+ wounds taken.
The bad:
Ather-khemists seem bad. Can't use their ability when garrisoned, or on garrisoned units. It's like anti-synergy with the whole army. They can't keep up with balloon boys, and that's the only real situation where you would want to use it.
There doesn't seem to be many command abilities you want to use outside of the admiral. The endrinmaster ones are garbage, for example.
Lists:
I think there will be 2 primary builds. Ships and Balloons (with ships).
The balloon build will take the new endrinmaster + a ton of balloons (taken in units of 6) + enough ships to let them hitch rides everywhere.
Ship build will use one of the battalions and focus on garrisons inside of a few bigger ships. This one is harder because points don't work out great in this book, IMO.
The actual list I'm thinking about is an Iron Sky Attack Squadron (2 frigates + 2x10 Arkanaut, 800pts), an Ironclad with 5 thunders + admiral + navigator inside (510 + 120 + 140 + 100 = 870pts), the new ballioon hero (220pts), and a unit of 3 balloon boys (leaning towards endrinriggers) for 100pts. Comes out to 1,990pts total. Not sure what sky-port. You could do Barak-Zilfin or take the Endrinmaster as general otherwise.