What's your first impression of Eureka?

[Kaonis]

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.

Except you're not done because death can make you lose a level. You even mention it later in your post, but I'll address it now. Losing exp and deleveling is an awful system. There is a reason MMO's moved away from that punishing mechanic a decade ago. Hell, even FFXI has eased up on that significantly over the years and was never as harsh as this. The slow leveling isn't even the core issue, the issues is the levels themselves are an arbitrary grind. Strip it away and nothing of value is lost. It's literally max level players being forced to re-level so they can fight stronger mobs. It could have been more interesting like say tying the elemental system to it by getting elemental abilities that you can only use in Eureka and are your core gameplay. But there's nothing substantial to leveling but to pad out the grind.

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.

On the bolded part I can agree. Though 2 main points. 1) Those grinds were better designed, if not by much. A lot of the time FATE's let you go on any job so you could at least level an alt while you do it. The light steps gave you more variety in activities despite repeating old content. 2) The major point I wish to make here is a lot of people griping on Eureka are also griping on

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.

Even WoW innovated their game every expansion. And innovating, at least their own game, is something MMO's need to do to survive. They aren't single player games to be done and forgotten, they are active games that are supposed to evolve over the years. XI was only as successful as it was because they kept adding new kinds of content over the years and pushed what was possible with their engine.

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.

It's up to players, it's always up to the players. Diadem died because all it was was a shallow carrot on a stick system. The carrot wasn't worth it so people quit fast. They gave a slightly better carrot this time (relic), but it ultimately won't be enough to keep players. Ultimately if people aren't having fun with the system then whatever reward you put in won't matter.

It's clearly not some mind blowing content and it obviously has been overhyped

There has been no hype. People have literally stated they just want it to not be Diadem, and yet it's what it is. If anything what I've seen from people is essentially "I had no expectations for this, and yet it still somehow disappointed me".

It sure has its flaws, but saying it's 100% garbage is dishonest.

You're right, the map is nice. So, about 99% garbage then.