I'll preface this by saying I love every expansion, and there aren't really any cards that make me upset. Some might be "blah" but I don't hate any of them.
1. Empires: This might be because it's brand new (I just got it this Christmas), but I am giddy about this expansion. I love alternative victory points and cards that encourage you to play in non-traditional ways, and Landmarks are this to the nth degree. This expansion also seems to encourage the people I play with to try a wider range of divergent strategies rather than just mirror each other. Finally some cards create new decisions: how long do I spin my wheels buying groundskeepers? Do I uncover the next card in this split pile? Will playing this gathering card help my opponent more than me? Etc.
2. Guilds/Cornucopia: I might even put Guilds here by itself, but combining it with Cornucopia makes it an easy number 2. I love coin tokens and Guilds has a bunch of cards that can do so many different things without having to list 40 different options on the card: (Herald, Stonemason, Butcher). I like Cornucopia for many of the reasons others have listed, and I even like Tournament, despite how swingy it can be.
3. Dark Ages: I just love how combo-y and bizarre this set can be. I even don't really mind the cards people love to hate here. Yes, urchin is almost a necessity, but it doesn't obsolete other decisions you make throughout the game. Rebuild can obsolete those decisions, but a Rebuild game is such a different way of playing dominion that I like it. Even in mirrors there can still be decisions, and beating rebuild with an engine or strong BM can feel great. Okay, maybe I would end up preferring the "or" version of Cultist, but I've never tried it.
4. Prosperity: This is the beginning of the solid expansions that I really like, but don't really get me crazy-excited when I think about them (just normal excited-for-dominion excited). What puts this above other expansions in this tier would be Colony/Platinum, victory tokens, and the additional non-attack interaction in the set (all even more reasons why I love Empires).
5. Hinterlands: Hinterlands is good. It doesn't really strike me one way or the other. Maybe the theme of on-buy/gain is a little too invisible? Or didn't seem as innovative/mind-blowing as other expansions' themes? I really do like a lot of these cards, but they aren't the ones I think of when I think "OMG I love that card!" Okay, I
do really like farmland.
6. Seaside: Durations are super cool, but I don't think the ones in Seaside really change the way you play that significantly; they're just good cards (Tactician is the stand-out from the set in this regard). The set also has a few duds such as Pirate Ship which is especially problematic because it can look so powerful to newbies. I'm especially disappointed by Embargo. It's such a cool idea that doesn't really seem worth it in practice. Also, it requires a bunch of tokens just for it.
7. Alchemy: I really want this to be higher. I think potions are a really cool idea, and I love a lot of these cards, but I do think I'd like some of these cards more with some tweaks (scrying pool without the spying, a limit of one turn for possession, maybe a +buy on Phil Stone?) That being said, all of them are cool enough that I'd miss them. Even the weak cards are still cool. Oh, transmute, how I wish you weren't bad. I think this is also hurt by being a small expansion. I'm in the camp of really wishing we could get an alchemy 2nd edition (bigger and tweaked), but I get why it makes no sense to do it.
8. Adventures: I really think I should like this expansion more than I have so far. Events are a wonderful inclusion in the game, but now that Empires suggests they might be evergreen, this expansion is no longer artificially inflated by them. I play most often IRL, and still regularly introduce the game to new players. As a result, I find the various tokens in this expansion too fiddly. Even the reserves can feel a bit fiddly sometimes.
9. Intrigue: I really like cards that can play a variety of roles, but I generally don't like using choices to do that. I think it removes some of the moments of discovery or epiphany that this game creates. I do really like the high percentage of alternate victory cards in the set, it's just that since almost all other expansions have them too, they don't affect this expansion's rank that much.
I think my opinion on Intrigue will greatly improve with the second edition, though. Some of the removals were great: Saboteur just felt bad for everyone including the person who played it; Secret Chamber was weak, the reaction was really fiddly, and it's outshone by other discard for benefit cards; and Scout was both boring and weak. Additionally, I really love some of the new cards although I have very limited experience playing with them. Diplomat and Lurker especially.
10. Dominion: The base game serves its purpose really well: introducing the game with a bunch of simple and straightforward cards. I also love how a bunch of the cards train you to become better at deckbuilders just by existing. That being said, I think this is the only expansion I can become bored of playing. The range of different decks it enables seems more limited. It also included a lot of duds. This is remedied by the second edition, but the replacements are just as vanilla as the rest of the set. I get why that's the case; I just don't get excited about it.
I know 'to each his own' and all that, but it's just really hard for me to fathom how much effect the art has on how much people like cards or sets. For me, the art is nice to have, but it makes almost no difference on how much I like or dislike cards.
I agree for the most part. Disliking a card because of its art or theme seems bizarre to me. That said, good or fun art can make me like a card even more. I especially like the conventions and callbacks that have developed in Dominion art and names. Things like Scouting Party or how cards named after small animals (Rats/Magpie) tend to multiply and ghosts place cards back on the deck (I wish Wild Hunt was named differently as a result).