1. Swamp. Enemies are varied in their ways of approaching you in combat. You have your humanoid melee and archer enemies. You have your bouncy, brainlessly stalking oozes. You have your sneaky wraiths. You have your large and speedy abominations.
The terrain is tricky in that you actually have to put some thought in how you navigate through it. The rain is a fair check to make sure you that you aren't taking half-measures when preparing your character. The only thing that sucks is when you need to go back to it to upgrade your blackmetal stuff and everything is weak as hell. But that is an overarching problem the game has with its absurd power-curve.

2. Plains. The most beautiful in my opinion. It has one of the only threatening bosses in the game. It doesn't outstay its welcome as blackmetal is easy to come by. It doles out rewards at a more satisfying rate than other biomes in my opinion. Needles are fun to collect and look cool when you fire them back at your enemies.

3. Mountains. It has enemies like wolves and fenrings who can counter your ability to step slightly backwards. Drakes are fun archery targets. Snowfall looks awesome. Something about running down their huge outer slopes after a successful expedition really gives the endorphins a kick.

4. Meadows. A neat introduction to the game. Teaches most of what you need to know very quickly. Perfect place to build a main home of course. The boss is too cool to be an underpowered tutorial boss but oh well. It is a neat touch that further out meadows can contain hazards like draugr villages. It loses points because one of the unfortunate consequences of doing what it is supposed to do, is that it is easy and brief. Deer hunting is kind of relaxing and I wish all of the biomes had this cat&mouse element in some form.

5. Mistlands. One nice thing is that it feels like more production value went into it than the majority of content that was there at the start of early access. But it exacerbates most of what I already didn't like about the game. It doesn't have enough content to justify how long it takes to grind out its expected progression path. And more severely than ever, enemies grossly outmatch you statistically, while also being to stupid to do anything. Its soft-barrier against sequence-breaking is also not what I would call a playful kind of frustrating. It doesn't up the ante with skill demands, just gear demands.

6. Black Forest. A very easy last place for me. It is a ridiculously long tutorial biome in a game that already has a perfectly serviceable tutorial biome. There is nothing I find fun about picking away at a dark hole in the ground while nothing can possibly throw a spanner into the works. Greydwarves and skeletons are ankle-biting pests.
Trolls are a cool spectacle and using them to bypass the need for an antler pickaxe is a feature that sounds fun on paper, but as a threat they are nearly as disappointing as everything else. They are ultimately just bigger pests.
It isn't just three times as much digging that needs to be done in this biome in order to get relevant metals for gear; you also need three times as much coal. You learn in this biome that in order to get said coal, you need to spend a load of time chopping wood and waiting for it to process in the furnace. This process that the game wastes so much time drilling into your gameplay loop becomes totally worthless for the entire remainder of the game once you get to the next biome and find a surtling geyser or two.

Seriously black forest nearly made me miss out on what came after. It has definitely deterred replays. It only kind of makes sense from a standpoint that this is the sort of game that you only play through once then never again. It has never been explained to me why survival games need to be stretched to MMO length. I thought retaining players in that way was all about raking up money from subscriptions and micro-sales.

Edit: Okay that last sentence makes it sound like I forgot that the game can be played in more ways than just solo, which for a second I did. Not going to remove it. Just owning up to a mistake. Still hate black forest.