Sorted by the wiki:
Kingdom Cards:Coin of the RealmI initially thought this was very weak, but now I think it is one of the strongest Villages in the game, and one of the strongest $2 costs as well.
Page Line I knew Champion would be good, but even the other Travelers are solid, though not as good as Peasant's. Champion is now the least fun card in all of Dominion for me, even less fun than losing a Cultist Ruins split 9/1, or playing 3 Rebuild games in a row. There's little thinking, only blind playing. It's just not Dominion when Champion is in play.
Peasant LineVery strong, and stronger than I first envisioned. I thought this would be weaker because it takes awhile to get to Teacher, but that is not the case. The only real drawback is having to play Teacher to get the bonus once every 2 turns, but this is okay, and not brokenly good like Champion. I also love Disciple.
All in all though, I am beginning to hate the Travelers. You almost always have to go for them every game they are in. If you ignore them, you lose. And yes, this is different from trashing cards because many cards can trash. Going for Page is like a more decorative Rebuild, it's so game warping. At least Peasant feels like you're making some rational decisions sometimes.
Ratcatcher It is much weaker than I first suspected, though it isn't terrible by any means. It just trashes .5 cards a turn, and you can only choose from your hand, rather than play it when you wish. If you could play it when you wished, it would be a lot stronger for me.
RazeI thought this card was going to suck so much, but it's even better than Ratcatcher, if you can believe it.
Amulet This card is worse than I expected, but not much worse.
Caravan Guard I still have yet to find a game where I have bought a Caravan Guard and not regretted the decision. It is a cheap Peddler when there are bountiful attacks, but the reaction is just so incredibly weak. It's a shitty money version of Caravan.
DungeonWeaker than Warehouse, though not much weaker.
GearI underestimated this card. It is quite possibly the best $3 card besides Ambassador and Masquerade.
GuideI underestimated Guide. Guide never hurts, and is better than Silver. It cycles, and it can help mitigate a bad stall as well. It never hurts to pick up a Guide. The only question is whether you have time to get one.
DuplicateSo incredibly slow to activate, and playing a Terminal with no instant benefits hurts a lot more than you would first assume. It is comparable to Saboteur and Sea Hag in how much it sucks in this regard. However, in a game with no gaining, Duplicate is insanely strong. In a game where cost reducers exist, Duplicate can even easily be a Province. This cannot be understated. All in all, Duplicate should not be picked up en mass until you're drawing your deck. Maybe one is fine. I think it is well balanced.
MagpieEveryone drastically overrated Magpie. It is not bad by any means, but it is not even close to the automatic Laboratory that people were afraid of, and losing the Magpie split will not cost you the game, only make it a bit harder.
MessengerOne of the most fun Dominion cards of all time is also (predictably) one of the worse cards. There are some parlor end game tricks you can do, but that's about it. And no, sending your opponent an extra Potion does not hurt as much as it helps him.
MiserI thought this card was going to suck. It's a fixed Pirate Ship. It can be used in an engine for sure. It is best to think of Miser as a Develop. If if is worth picking up a Develop to trash coppers only, it is worth it for sure to get a Miser.
PortStrong strong strong engine enabler. I never doubted this.
RangerTechnically 'weaker' than Smithy, you give up one Action card for a fantastic play later, a la Tactician, and you also get a free +buy. I wish the second play of Ranger also gave +1 Action to make the analogy complete, but that is that. One of my favorite cards, which is why it was my avatar for awhile. I also keep forgetting Ranger is a source of +buy. Ranger Big Money sucks.
TransmogrifyAbout as strong as Remodel, maybe less. It is so incredibly slow, you do not want more than two at the most. I had this card rated higher before, but every time I overbuy Transmogrify, I regretted it. Visions of piling out the Provinces with Transmogrifies ended in only sadness, despair, and jsh's phantom voice laughing over me in sheer delight, that devil.
ArtificerIt kind of sucks. It's not worth $5 for the effect, but it's worth more than $4. It's fantastic with Tactician for a guaranteed Province, and there are some parlor tricks you can do with engines, so it's not all bad, but it is underwhelming.
Bridge TrollWho knew that a lack of virtual coin actually hurts a lot? I sure didn't. The attack isn't that great, which is okay! The nice bit is that it can really enable engines due to the duration aspect of it.
Distant LandsI had this card tremendously underrated. Seriously. People hyped it up, and then I played some games with it, and I hated it afterwards. Turns out, I was only using it wrong. It's a fantastic game warping alt-VP card.
GiantI thought I'd hate Giant. I don't. I love it. I wish there were more Dominion cards that used the Journey token.
Haunted WoodsI thought the attack was lame, but you really don't understand how evil it can be until you play with it.
Lost Cityif you're going to want tons of Lost Cities, get them all in a single turn. Get the pain over with. I had this card about where I think of it now.
RelicWow, is this card better than I thought. It's not the best attack in the world, but it hurts a lot more than it feels like.
Royal CarriageThis proves my theory that you'd pay $5 for a Throne Room. It is a little weaker than Throne Room, sure, but it is a bit more flexible and gives you more options. However, not being able to chain Thrones kills the mood, not to mention the art is so terrible, jsh would pimp-slap whoever did it.
StorytellerI am still confused about this card, and I think it will be this way for a long time for many. Still too early to tell, but I think it is on the weaker side.
Swamp HagWeaker than I expected. It doesn't stop megaturn engines much at all, and if you're wasting time getting this, it means you're desperate and behind.
Treasure TroveWOW did I underrate this card. I thought it would be like Cache, but it's so much stronger. If Treasure Trove and any draw is available, consider going for that over an engine. Seriously.
Wine MerchantIt's like Baron, but suckier due to not being able to open with it. It has its uses if you need instant payload though. I still think it's underrated a little tiny bit, but that will not be realized until much later on.
HirelingWOW did I underrate this card. Much much much better than Gold. I don't know how many Hirelings is too many, or when to stop getting them and start winning, but a good way to think of it is how much you are drawing your deck. This card makes it more likely you do, and faster.
Event Cards:AlmsPretty much where I expected it to be, very strong in the right situations. You can even get Gardens with it, and Tactician loves this card.
BorrowGetting an extra dollar at any time is fantastic. It even has the feeling of debt hanging over you, to where you want to use it every turn to mitigate the loss of card. It's worse to have one less card over a dollar, but I love this card anyways.
QuestProbably the weakest of the Events, though it has it's uses and it is $0.
SaveSo flipping strong, even at $1. Save changes the game, almost game breaking. Not even kidding.
Scouting PartyI thought it was a little weak at first, but I have now decided that the card is actually very good and for very cheap. And who can deny the art was really well done? I mean, look at this fantastic rendition of a Scouting Party:
Travelling FairI undervalued this card, but for the wrong reasons. It's great, not because it can top deck, but because it gives buys.
BonfireGreat trasher. Yes, you'll spend $3 to get rid of 2 Coppers. Much better than Silver.
ExpeditionI still think people underrate this Event. It's so freaking good. I underrated it before as well.
FerryNot as broken as I thought, and it's more fun than I thought as well. I thought I'd hate this event.
PlanStill underrated, but it is not incredibly strong. This card confused me for awhile.
MissionIt's either OP or meaningless. Try using Mission in games with Cultist, Torturer, Mountebank, Rebuild, and other cards that will have people rethinking their relationship with you!
PilgrimageThis is so incredibly underrated, possibly the most underrated Event ever. Like, people do not understand that
spending $4 twice to get 3 cards of your choice is just flipping fantastic. The only question is when to buy the first dud, which is a total turn off.
BallI think it is still undervalued. I cannot say enough that you can buy this as many times as you like with no penalty after the first one.
RaidIt's alright, not the worst Event of all time. (Don't tell anyone I said this, okay? I want it to continue being a joke)
SeawayI underrated it.
TradeAbout as good as I expected it to be, as in not very great at all. It has its uses, but it's going to be a very poor engine game for you to want this most times.
Lost ArtsI underrated this.
TrainingOverrated.
InheritanceUNDERRATED.
PathfindingUnderrated.
And that's about it, folks. You can take your tickets and demand a refund now.