I feel that I've played with them enough to have a reasonably informed opinion now. So, with all the usual "based on my experience, your mileage probably varies, and so forth" disclaimers on the table and in no particular order...
>Amulet
Honestly, I think this one has hit the table every time we've had a "draft" (every player picks 1 card for the kingdom until there would be a remainder, so for our usual 4 players every player picks 2 and then then remainder are random). I've probably done more theory work on it than any other card in the expansion; if I was picking a card from the expansion I'd want to write a strategy guide for, this would be it (for the record, I'm nowhere near good enough at the game to try this yet). I haven't run into too many cards that make me think as hard about what to do in the standard 3/4 starter draw as Amulet has ended up doing.
>Inheritance
It's as if they held a competition to create a card that would convince us to actually buy Estates, and this is the card that won (*Disclaimer: we still don't have a copy of Intrigue in our group, it seems to be perpetually "the next expansion one of us ought to buy"). The craziest combination I've seen in-play so far was Marketplace, and that was nuts.
>Distant Lands
Disclaimer, I've turned into a sucker for alternate victory cards. I think buying Prosperity as my first expansion spoiled our group; we've ended up always using a 4th victory card & 4th treasure card because we got used to it early on. As such we're probably seeing this more than other groups do, since it's coming up in about 20% of our games. It led to one of the more 'foundational' questions in the game yet ("Hey, how literally are we supposed to be taking these "put on the mat" cards? If you used Island on Distant Lands, would DL be worth points or not?"). We decided on "Very literally", just for the record.
>Disciple
I had some good experiences with this card early on when we started with Adventures and that probably still colors my opinion of this card; it's definitely my favorite Traveller right now. I've had one game where I got to three copies of it in deck, and it wasn't to keep someone from getting to Teacher. I won that game on the strength of Disciple + Distant Lands, for the record.
>Ferry
...And suddenly, it mattered whether you started 3/4 or 4/3. I do think it's interesting that we see the -2 cost token move around a lot more than any of the others.
HONORABLE MENTIONS
Ever look at a card, go "I bet there's an interesting interaction here, I'll have to go looking for it", but somebody beats you to it? That's Travelling Fair in this expansion for me. It had some obvious recursive potential but I ended up being too interested in other cards (cough Amulet, cough Inheritance, cough) to look into it enough before others found the path.
Alms also gets a special nod. I think I've mentioned before that one of the players at the table is perhaps overly fond of Thief (even after having been beat with a treasureless strategy). She hates this card now.
DISHONORABLE MENTION
Yeah, this is supposed to be favorites but... Guide. I think I've seen this card backfire as often as I've seen it be useful. I did see one weird case where somebody did this with Inheritance and a +Buy token that actually almost worked but... it's been way less useful in practice than it looked going in. I hate to call it a disappointment and I won't call it the worst card in the expansion, but it is the one I like a *lot* less than I thought I would.