The word Geyser comes from Icelandic, the first documented geyser, was named Geyser and is in Iceland. I have not been to Yellowstone, I saw my first geyser in Iceland last spring.
Geyser rarely erupts, but the one next to it erupts every 8 to 15 minutes. Not quite set your watch by it, but often enough that you can stand around and watch. We did. I found it fabulous.
There is an amazing hotel across the street from Geyser, the next time I want to stay there. They have massive four wheel drive tundra tours from there, I want to ride one of those. They look amazing.
There are many things left to see. IcelandAir has first class, off season fares of $999 round trip. I can't do it this fall, but spring will be here before we know it.