I have a lot to say about the new cards. I will start with the removed cards first (Base and Intrigue), and then I will get to discussing the new cards in proper detail.
Secret Chamber: I'm probably one of the few people who actually likes Secret Chamber's on-play effect as a card. It worked well enough with Scrying Pool and Tactician decks. However, Storeroom and Vault do the same thing but better. Secret Chamber will not be missed. The reaction is just plain awful.
Great Hall: People always talk about how much they love Great Hall. I don't get the love. It's a cantrip Estate. What's the big deal? It's pretty awful design, and it's something you buy when you have nothing better to buy. Never a good way to design a card. Sure, Mill isn't great, but at least it provides options sometimes. Great Hall is just plain boring, which is the worst crime a Dominion card can commit.
Coppersmith: Out of all of the Dominion cards replaced, I am going to miss Coppersmith the most. Let's face it, Coppersmith's effect is really cool. If it only had a +buy, it would be a lot stronger. A lot of players play with this once or twice and then give up on it. I think it is worth salvaging for another expansion, and I am certain Donald will do some refreshing take on the concept then.
Scout: Scout had to go. It is the worst card in Dominion.
Saboteur: Saboteur had the amazing ability to make you very angry at your opponent while still knowing you would just likely win the game. Saboteur is just a pure awful card. It's not fun getting hit with it, and it's not fun to use. Even Swindler is a card that is fun to use sometimes, even when I have such a mixed relationship with it.
Tribute: I wish Donald had kept Tribute, or perhaps just buffed it. It was a weak card, but I will have more to say on this when we reach Courtier.
Adventurer: This card needed to be replaced. It was almost never good. The only time it was nice is when Venture basically did the same thing but better, and for cheaper. Adventurer might be just as bad at $3. It's basically a 'can't miss' Moat draw, and it also skips Actions to boot. It would be a fine BM card then, at least.
Spy: Spy is not a fun card, and that is its gravest sin. Spy is fine enough as a card, although it is a bit on the weaker side. However, waiting for ages for the opponent to make a decision with multiple Spies on Dominion Online implementations was the worst thing since Pol Pot, so I am perfectly fine with this card burning in development hell for eternity.
Thief: Thief is just plain ol' awful. I don't really have to say anything about Thief, do I?
Feast: I had a proposed fix for Feast where if you trashed it as well, it would do the same effect as if you played it. This would make it a bit stronger for trash-for-benefit, as well as you not being too sad with a Chapel/Feast opening collision. See? Feast is kind of awesome then! I think the Feast card could be fixed somehow in some way, and I hope we see another variant of Feast in the future.
Chancellor: I like deck discarders a lot, but now that we have Scavenger and Messenger, do we really need Chancellor now? I know I speak for everyone when I say we will miss that butt chin.
Woodcutter: A sad card. Out of all of the cards, Woodcutter was simply the most likely to get canned.
Now onto the new cards.
Courtier: This might be worse than Tribute. At least Tribute provided +Actions in some engines. Courtier does not provide anything of use besides a sucky +buy. Courtier proves that people will pay $5 for a +buy. Courtier is a 'suck it up you loser' card. It also buffs Dame Josephine.
I feel like people misread this card sometimes as well. Courtier will be nice with cards like Bridge Troll or other Attack Durations. However, out of all of the new cards, Courtier is likely the saddest of the bunch.
Diplomat: I hate this card too. It's a really eh Reaction. It's basically the fixed version of Secret Chamber's deck inspection. It's still word hell. Draw two cards and if you have 5 cards you get +2 actions and when someone plays an attack card you get to draw two and discard three and I still hate it. Imagine using this card as the only village though. That would be kind of a neat challenge.
Lurker: This is the ultimate $2 card. It's a fine opening on a $5/$2, and it eventually pays off. It's lumbering and slow, but I do enjoy this card very much.
Mill: Why does everyone hate this card? It's so much better than Great Hall. Oh no, you might have to discard two cards and get $2 out of it. It combos with so many draw to X cards, and it's also choice based and makes you think, unlike dumb ol' Great Hall. I love Mill.
Patrol: This might be a great BM card. It makes your next turn a lot better. It can draw upwards of
seven cards on a single play. Might be one of the better draw cards in the game. Journeyman is a bit better for engines, but I cannot help but compare Patrol with Journeyman.
Replace: The Remodel we have always hoped for. It's a Remodel with Benefits. It won't ask you for anything in return. It won't bring drama into the home. You can topdeck Action cards and Treasures, or get Provinces and hurt your opponent. It's not a fantastically great card, but it is a good one.
Secret Passage: We lose one horrible card with Secret in the name, and now we get another awful card with Secret in the name. More waiting for the opponent to make the decision on what to discard and where in the deck to discard it. I cannot wait. Ugh.
Artisan: The new 'Feast', although it is more like Altar. I am not certain it is all that great, but it makes you think. It can get Duchies and unlike Altar, you don't have to trash to get them, which is a bonus. Something I have not seen talked about, the card you gain can be topdecked!
Bandit: I don't know why, but I am in love with this card. I know it's not that great, but I just can't help but just like this card. It makes me smile just looking at it. Maybe it recaptures that first Thief game I had. Maybe it's a nostalgia thing. I don't know.
Harbringer: We all knew this card was going to exist one day. All of the experts tell me it is not very strong. I say it is in certin situations. You can chain together a singular Goons every turn (until you shuffle), and you can combo it with other cards as well. You get to topdeck that Fortune over and over. Followers. Trusty Steed. A key draw card. It's versatile. I like it. Many interesting options.
Merchant: Another card I really like, despite being very simple. A super cheap Peddler on the condition that you play a Silver. An engine can support a singular Silver. That's not a problem!
Poacher: Basically the same thing as Merchant, but guaranteed. It also sucks if you emptied them. If your opponent goes mass Poacher, you can punish him by emptying the pile. Poacher makes you not Poach too much, or else you face consequences. It's so thematic! I love it, even though it's pretty much the same as Merchant in execution.
Sentry: WOW this card is strong. It is stronger than Junk Dealer. There's nothing else to say. It's absurd how good this card is.
Vassal: I love that this card is a lame Herald. I also love that it combos with Harbringer and other cards. You also don't have to play the Action card you discard. Options. I like it. This is what Duchess should have been.
Those are my thoughts.