Cultivator's Caravan: Is just excellent. I wasn't as excited about the art-it's not bad but that's OK. A good card is a good card.
Combustible Gearhulk: another very good card. I like how the red in the picture is subdued, and not the dominant color. The rating is just good though because the opponent's choice is almost always going to be obvious (milling for damage) and that could be big, could be nothing.
Saheeli's Artistry: The art first: again, I like how the blue seems subdued for a blue card. The effect is excellent as well, though I think the flavor text is a bit bland.
Toolcraft Exemplar: continuing the theme of solid art here, too. This is a fair card I think. It doesn't take much to make it good but it takes a lot to make it excellent.
Thriving Turtle: I think this is a good card. It can be a 1/4, or it can be an energy battery and blocker for one blue. That's solid. Everything else about the card was merely fair but it'll do.
Longtusk Cub: I'm going out on a limb to say it's an excellent card. Repeatable energy battery plus the ability to grow at instant speed? This reminds me a little bit of Jitte and that's a good thing. It's always going to be a threat and that makes for a very solid card.
Ruinous Gremlin: I really like the flavor text here, because it gives me a sense of Kaladesh. The card is a good effect too: solid early as a "rattlesnake" effect, useful late when they have you up against the wall with a Skysovereign.
Aerial Responder: Little too much white in this picture for me. Contrast still matters! But the flavor text adds to the plane and calling this the White Vampire Nighthawk is not out of line. It's great.
Smuggler's Copter: so good. The art is a little weird and it obviously can't carry much for smuggling but I have a feeling that this card is going to show up in decks the entire time it's in Standard.
Sequestered Stash: While I like the art and the implications of the name, the ability really isn't all that. Marginal card. If it didn't require a sacrifice it would move up considerably...and it would also make dredge completely broken in Modern. Still, a marginal card is marginal.
Brazen Scourge: Washed out pink art! It's like an attack of Pepto Bismol. But 3/3's for haste are good. I don't know if this will help the R/B aggro deck that WotC thinks is there in draft, beyond the draft format but who knows? I would very much like to see R/B at the top tables for awhile: it's the only color combo I can think of that has never really had a day in the sun.
Highspire Artisan: I don't like the artwork and I don't like this card. Washed out green tones everywhere, and the option to get a 0/3 and a 1/1 or a 1/4 just holds zero interest for me. Sideboard card in limited, if that.
Contraband Kingpin: I think this card is excellent. Slides well into a U/B artifact deck and does precisely what you hope it will to give you: time. The artwork is very cool, too and I'm excited to see a new creature type with this kind of style.
Demolition Stomper: boy that artwork is drab and brown against a dull green backgrowd. For a plane that is supposed to have slick, lively vehicles, this sticks out in an ugly way. The card itself is marginal, since 10/7's that can't be chumped...hm.
I may have misevaluated this card. A 10/7 will probably take out anything that's put it its way and opponents can't just hope that their 1/1 tokens will give them time. I should test this one.
Rush of Vitality: This is a weird card to see in Black, so I rated it good. Indestructible isn't something I think fits the color often but since they're using Indestructible to replace Regenerate I think it'll happen more often. Thematically, it doesn't work but mechanically it's probably better so I can't argue with that decision. Indestructible is also better than Regenerate for the most part and the artwork feels a lot more colorful and dynamic than what I often see on Black cards.
And that's it! Overall, I'm still pretty interested in this set and want to see how it interacts with the rest of the game. I'm hopeful that it'll be a very solid set, even if it doesn't introduce anything incredibly game changing.