(Though to be honest with you, the first 45 seconds of the episode spoil all of the first series for you. If you haven't watched that first, you really should. Both to avoid spoilers, and because it is just amazing.)
So, let's assume you've seen the first series. We now know that The Good Place is The Bad Place (Mwahahaha!) and our four main characters are being tortured by Michael and all of the other occupants of "Paradise", who are demons in disguise.
The demons are great fun now they can reveal their true selves. They're torn between love of torture ("can we start biting them now?") and being slightly whiny actors who are annoyed that they can't keep the same roles as previous. (Real Eleanor in particular is terrific as a new pizza restaurant owner who can't find her motivation.) Michael is also fun, as his slight incompetence is balanced against a Machiavellian scheme to improve the torture.
Nicely, the show keeps its cheerful, slightly relaxed feeling, even with the knowledge that we're now in the depths of hell. Somewhere so terrible, it has "butthole spiders". I really would be interested to see what the traditional hell is like. There's a shedload of backstory here that we'll probably never see, but is really quite interesting to ponder about.
The main four have been reset, with their memories erased, but everything else continues on, with all of the consequences affecting the world around them. It's a fun twist, which is going to let the plot expand into interesting places. We start to see how hell preys upon people's fears, and it's really rather clever.
Still the best comedy on telly currently. Though needs more Janet.