It seems beautiful, but saying unparalleled is a little hyperbolic. Western Norway, Switzerland, Northern Scotland, and the North American Rockies all appeal to similar sensibilities and arguably just as grand, if not more so in some cases.
There are no trees in Iceland. It's fine to look at for a week and the northern lights are a novelty, but the US and Canada (even California alone) offer much much more in terms of nature.
There are definitely trees in Iceland. Not many, not everywhere, and not impressive ones, but they exist.
However if you've been to Iceland and thought there wasn't much outdoors, I'm not really sure what to say. It's sparsely inhabited, beautiful, and gigantic. It's a totally different experience from something like the sierras.