Ost-In-Edhil and the lands of Eregion
 

We don't have much to go on how the region looked like and were. But did the lands of Eregion, when they were populated by the elves, had the same timeless and ethereal feel of Rivendell and Lorien? Or was it more similar to the Shire with it's calmness and Ost-In-Edhil had that grand and splendind visual where the sun shined upon it? Making it looked more ethereal.

Probably.

Elves tended to have that effect on the places they lived.

This is cited in Fellowship.

The "timelessness" of Lorien and Rivendell was attained largely by the use of the two rings of the Three used by their Elvish guardians. Eregion had no such powers at work.

The Shire had a wholly different feel due to, I believe, the nearness of Bombadil, and its proximity to the Sea.

Eregion I see as more akin to First Age Nargothrond: impressive in graceful strength, but more "industrial", owing to the Noldorin focus on crafting.
Legolas noted that he could "hear" the stone of Eregion recalling the Noldor, but that to himself they were "strange".

x/d with Kuru

Isn't it possible since Celebrimbor was the maker of the rings, he too could have used his powers on Eregion? Maybe not the whole of the realm, but Ost-In-Edhil and it's surroundings nearby?

And by the way, Nargothrond was a underground fortress right? Ost-In-Edhil is not, so since you said it has that graceful strength and were industrial, maybe it's similar to Minas Tirith.

Quite possibly a comparison with Gondolin might be apt for Eregion.

But if so, not in a lasting way. We know that with the loss of the Rings' power, Lothlorien became just an ordinary forest. Moreover, Celebrimbor could not have used any of the Three Rings for very long, because as soon as the One was forged he hid them (and none dared use them for the rest of the Second Age)