Part of what makes the sounds so realistic aside from the stereoscopic 3D audio, says developer Franz Bruckhoff, is that the nature sounds are from Emmy-award-winning nature sound recordist Gordon Hempton. I'm frankly not familiar with his work, but I can tell you all of the storms sound very realistic in Thunderspace.
One issue I noticed immediately is that you can't set a sleep timer. But Bruckhoff says the feature is coming soon and will be available in a future update.
While this niche app is likely not one you'll use on a daily basis, Thunderspace is great for a little relaxation in the dark with headphones, and the lightning that's timed to precede the thunderclaps makes for a great thunderstorm experience.