My group had a great time in the adventure and an epic finish. They (and myself as a GM) are relatively fresh to the pen and paper world, but I found John's writing and encounters and the overall situations adaptable to their skill level (and mine).
The Sun Below is a great setting in a great game world and it meshes well with MCG's established, official supplements. Sufficiently alien, but it doesn't feel illogical and too great a leap to believe it exists in the Ninth World. Marvin brings enough weird, but leaves room for you to bring more -- for me, as a GM, that's important for Numenera. The encounters are scaled nicely, as well, with notes for lower and higher level characters' abilities.
Though this is, ostensibly, a follow-up to The City on the Edge, my group hadn't run it when we were given the chance to test this adventure (I was setting it up as a possible route for them to take, however). I was able to introduce the characters without too much trouble and make it work even without their prior knowledge of the Sun Below and the few recurring characters here. Given how they ended things, I'm not sure how I'll get Lebby into City on the Edge when they inevitably return, but I'll keep it weird whatever I do.
In short(er), if you play Numenera this is a great adventure whether you've been to the Sun Below before or not and there's a lot of good ideas to pilfer even if you don't run it straight.