I wrote this pretty quickly, I'm not as sure of these claims as I am of the $2-$3 cost thread. I intend to get to the rest of the Adventures cards and events when I have time to.
Duplicate: I've had trouble using this card well, but I think it's better than my experience would suggest. Buying the Duplicate and spending the action to get it on your Tavern mat is so clunky. That being said, it's very useful to have it ready to call in endgames, because threatening a Duchy duplicate is quite hard to play around. In my experience, I buy it and lose, or skip it and also lose. I don't think you should open Duplicate, but you may want to buy it 2nd shuffle.
Magpie: At preview time, people held Magpie up as really really good. It's good, and I usually open 1, but if you want to gain more Magpies you really want to buy 2 Magpies - buying one just isn't consistent enough. The problem is that you can get baited into buying the 2nd Magpie in your 2nd shuffle, and other $4 costs can be more important. Note that once Magpies run out, they're only better than cantrips if you reveal a Treasure. You can't ignore Magpie, but if you get other actions in exchange for losing Magpies 4-6 or 3-7, it's not the end of the world. Becomes very important if card tokens (+1 Card, +$1) are in the Kingdom.
Messenger: A card you buy because you need the +Buy. On-buy is important for 3 piles. It turns out you can't do too many cute things with the on-buy effect, because any cute things you could do get offset by having to pick up this Woodcutter-Chancellor as well.
Miser: I have nothing to say about this card, because I've only bought it once, and I've only had someone buy it against me once. Weird, right? But it's true.
Port: A really nice village for engines. If it's the only +Actions in the kingdom, remember that you either do a 6-6 split or a 8-4 split, and it only takes 3 or 4 buys to get there. If you think you'll want more than 4 Ports, you need to buy them fast. Like Magpie, becomes very important if there are card tokens.
Ranger: Try to start your turn with the Journey token face down, to make your first Ranger give +5 Cards, because this helps a lot of reliability. You might think that means you should target buying an even number of Rangers, because if you play all the Rangers you'll always end back at face down. In practice you should just think of them as Smithies, because you'll inevitably fail to draw all the Rangers in your deck. If you ignore the Journey token, and pretend their Smithies with free +Buy, you'll be 80% of the way there. (Also, remember Ranger, Giant, and Pilgrimage all share the same Journey token! This is surprisingly easy to forget.)
Transmogrify: I like this card a lot. I think people weren't impressed with it at preview time, but I at least have turned around. Early game Estate -> Silver in hand is really useful. In one game, someone opened Transmogrify/Urchin, played Transmogrify T3, then did Estate -> Urchin to gain Merc turn 4 without having to open Urchin/Urchin, which actually blew my mind. Late game you can trash any card into itself to run down the pile, and much like Duplicate, it's hard to play against an opponent that could empty 3 Provinces in a single turn by calling 2 Transmogrifies. That being said, the 1 turn delay does matter, and it's really only good at trashing Estates. I basically always open 1, pick up a 2nd pretty often in engine games, and sometimes buy a 3rd as well. If the card weren't so hard to play well, I'd have written a full article about Transmogrify.
Artificer: The gaining effect isn't as good as it looks, because in many games you can only do the discard once before you run out of cards. But the worst case is still a Peddler. Don't buy a lot of them unless you plan to use the discard-for-gain effect a lot. Works well with draw-to-X and Scrying Pool. Remember you topdeck the gained card!
Bridge Troll: Because it's a Duration, you only need 1 +Actions for every 2 Bridge Trolls. At least in theory. In practice, you want a bit more than that for consistencies sake. Because you don't get the +$1 that Bridge would give you, and because your opponent's Bridge Trolls are giving you -$1 each turn, you can't neglect money entirely. You want just enough coins to use all your Bridge Troll buys.
Distant Lands: Very good. In money games, you buy this over Gold pretty quickly. In engine games, these should be your preferred source of VP, and you should start buying them earlier than you would normally green to give time to get them onto your Tavern mat. In engine games, it can be very hard to win if you lose Distant Lands 3-5 and they get all 5 Distant Lands onto their mat.