The 3D Classics version of this was the first Kirby game I played, though since then Dream Land has become strongly my favourite.
Since Adventure introduced the copy mechanic, among many other changes, I'd thought of this as being the point where it all went downhill, and when I replayed parts of the 3D version, my mind didn't change.
But playing the original (on the Switch) has greatly changed my mind; this is a really, really good successor to Dream Land.
I really like the 3DS' 3D, but, if I'm remembering correctly, that version of it removed the slowdown, which adds a lot imo. Though at some points it really is too slow (especially during inhaling, which unfortunately serves as a reason to just use copy abilities, whereas in Dream Land it worked excellently for encouraging only inhaling when necessary, at the last second).
The bosses are all great, but all of the minibosses are more just annoying. I'm not really sure why that is but the divide seemed very clear. The minibosses don't ruin the game or anything, and the good bosses more than make up for them.
Almost all of the copy abilities are fun to use, which is not something I'd say of many later games. My favourites in particular were the parasol and sword. I think they all had annoying downsides though. Attacking with the sword while moving leads to walking into the enemy if it survives your attack, and it's the same with dropping downwards with the parasol. Neither of these are unfair but they are less fun than they could be as a result.
Being able to run and slide are good new additions. I think this had more powerful stars for when you inhale multiple enemies simultaneously? If so, that's really good also. While I don't like the copy ability much since it comes at the cost of the focus on inhaling and firing enemies, it's perhaps fitting that a major new mechanic like that was added, and it could've been far worse.
Still, the elements that are inferior to Dream Land stand out more to me:
-The field of view feels way too large, making the game feel much slower. I think it also made the level design less enjoyable, with a more open view leading to more space unutilised, though that may also be down to there just being more levels in general
-The increased length means this is nowhere near as replayable (at least not right the way through) as Dream Land is. If there was a truly improved successor to Dream Land of a similar length, it would probably lead to Dream Land being made obsolete, so I'm a little glad it isn't. No part in particular stood out to me as demanding a replay, besides maybe the final boss, so I probably won't be going back to replaying individual sections since I'd need to decide one.
-Water isn't fun.
-Dream Land's only flaw imo was those exploding enemies. They don't stand out anywhere near as much here, since everything else was already slowing you down already, but they're back.
Overall, I think it's about as good a sequel to Dream Land as possible, though it's still not quite as fun.


EDIT FROM A FEW DAYS LATER: I think I've changed my mind actually. For the actual engine, it does play very similarly to Dream Land, and it does have improvements, but the ideal sequel to Dream Land really could be the same length as the first, so long as the gameplay was changed sufficiently in a positive manner.
The copy system here is still the best version of it in the series, but it's still not really that fun. A lot of fluidity is lost in its usage. I'm not sure what kind of system would work, but maybe even the sprinting and kick sliding would make enough difference to differentiate a sequel. Either way, it's incomparable to Dream Land.