I have all 5 of these on Audible as well as Kindle. I find them very appealing, and with the wide cast of actors that give an incredible range of voices to their characters, I listen to them frequently.
Since I read these in Kindle format first, it was rather startling that the voices were SO very different. Now I can’t imagine them any other way.
This is the starting point for the series, so give it a try. The aliens have conquered Earth, killed most of humanity, and are using the survivors for a big competition/game that also has alien competitors. The aliens constructed a series of dungeons underground divided by floor levels, and the surviving players take stairs down to the next level when time is up. You have to go, as the floor you are on will collapse.
The challenges increase as you descend, but so do the attributes granted in game play to improve and upgrade the players and their abilities.