Yellowstone is amazing because it has such a diversity of nature. None of them in and of themselves is unique to Yellowstone, i.e., there are geysers all over the world. But Yellowstone has a number and combination of interesting nature features, including over 100 geysers, that probably no other place on earth has.
People who have seen the variety of geysers there say Old Faithful isn't even the most impressive geyser at Yellowstone, just the most famous one, probably because it's the most predictable amongst the big ones. Grand geyser is typically the tallest and most impressive one. It's just harder to predict and the interval between eruptions is longer, so not visited as often.
And I didn't say Old Faithful isn't amazing, just that it's not worth fighting the traffic and crowds and problem of trying to get a parking spot you'll typically get there unless you're willing to go really early in the morning, which we may decide to do depending on our other priorities at the time.
Everyone should know better than visit or not visit, see or not see a place based on what a person on the internet says.
