What's your first impression of Eureka?

[Krotoan]

It's actually not. Once you hit Lv.20, you're done forever. At least until they raise the level cap (if they even do it). The elemental level is shared by all jobs, so you only have to level once. Except if you die a lot without getting a raise, obviously. I made 72k EXP in two hours yesterday. That was enough for a level. I expect that time to increase a bit, but not much, as people will keep being able to spawn higher and higher Fates.
Compare that time to the other kind of leveling systems there is in FFXIV, and you'll realize that the Eureka one isn't that bad.
This is subjective. I find leveling my other jobs in PotD to be very boring and brainless. On the other hand, I enjoy leveling in Eureka, for multiple reasons. I'm not saying that this is the pinnacle of fun by any stretch, but grinding Fates in N.Thal, getting Atmas, doing books, gathering light, going A1S again an again, doing years old content, and so on... isn't what I'd call "fun" either. I'm just aware that I'm playing a mainstream WoW-like MMORPG, which helps not raising my standards too much. If I wanted true novelty and innovation, I wouldn't be playing FFXIV. So, I'd say that people's standards and expectations are part of the issue.

PoTD leveling has always been a weird point for me. People say it's the most efficient but I cannot for the life of me bring myself to PoTD for that long , over and over. I'd rather daily roulette and beastman quest. Varied experiences with changing mechanics and pauses in between. For someone like me, Eureka is that PoTD grind but it's the ONLY way to get those levels. That's why I have a problem with it.

Call them trash if you want, but they won't hesitate in one-shotting you faster than God Kefka if you are careless. Besides, almost all the "trash mobs" have different kind of attacks. Some cleave, some have ranged AoE, some petrify you, some apply a potent poison, some jump all over the place... Even if it's small, you have to adapt to them in some way. The terrain also plays a part in this.
Sure, it's still farming trash mobs. But a lot of FFXIV is actually exactly that, would it be dungeons, fates, PotD...

I mean, they hurt worse than overworld mobs, but anything but NM's aren't going to one shot you. And once you find your flavour of the .. next 20 minutes it's not going to change and you can autopilot the everliving hell out of it. Trash mobs ARE trash mobs, but dungeons mix it up from pack to pack. Eureka is just a long drink of lukewarm water.

If there was no penalty for dying, Eureka wouldn't feel threatening at all. There is danger because the consequences of your death do exist and are harsh. And I absolutly doesn't see any other method to make you feel that way.
Another thing to note is how people have responded to that mechanic: players are actually helping each other. They will raise you because they expect you to do the same for them. Since there's absolutly no competition and that the most efficient way of doing things is to cooperate and be helpful, well, people are actually doing exactly that. Frankly, it's been a while since I entered an instance with so much positivity all over the place. You may not like that mechanic, but you cannot deny the good things it generates.

You know what would be a good penalty for dying? Getting warped back to the starting point and having no aetherytes except the main one. MAYBE make it so if your party is still alive they can res you but once everyone is out of battle , pewf, homepoint. You miss out on some XP, you gotta walk back, you maybe miss out on the rest of the NM because you can't get back fast enough. Cost, danger and no 2 hour setback. People rez-ing others simply because they hope to god someone else will do the same for them since the death penalty sucks so very badly is not a positive for the game, it does give me hope for the playerbase though.

Frankly, this is up to SE. If they keep updating it with new rewards and keep the thing living. But, as I already said, it's already an effective method to get some not-so-bad gear for alt jobs while tomestones and raid equipement is still somewhat precious. So even if the numbers drop, it should still be populated enough.

If the formula never changes there will be the people farming at 20, and then a scattering of people trying to level solo to 15 or so when they'll be viable for the 20 people to pick up. Ideally the lowbies will group up , but since disparity in level is so harshly punished this seems unlikely. True its not a bad way to gear up an alt job quick, but it's not like you're going back to old content to do it. You'll be farming the 20+ NMs.

So, overall, I think it's fine. Really.
It's clearly not some mind blowing content and it obviously has been overhyped (I still think that people are somewhat responsible for their own expectations though)... But it's not a disaster either. The map is great, the feeling of danger is somehow refreshing and brings good player interactions, the monsters (both trash and NMs) are interesting enough. While the rewards are lacking, gearing my alt jobs is enough to keep me interested... and hopefully SE will update it right in time when they need to.
It sure has its flaws, but saying it's 100% garbage is dishonest.

100% garbage? Of course not. A lot of things I personally don't like and wish I didn't have to deal with for the rewards they've locked behind it? Most definitely.