As per your request, I haven't read any of the other responses yet.
I read the book Jonathan Livingston Seagull when I was like 17, and recently reread it just to make sure I wasn't just in a strange teenage haze when I read it, but I loved it then and I still love it now and it has kind of shaped the basic idea I have for the afterlife, IF one exists. A lot of people think the book is trash. There are parts I find... meh... but the overall idea, I love. It has something to do with your afterlife being based on what you did in this life, and your second afterlife being based on what you did in your first afterlife, and so on. This is what I took from it, and though I still haven't decided whether or not I believe in the afterlife, I think and hope that is what it'd be like if one does exist.
And it makes sense, too. I feel like, if I'm happy in this life and achieve good things, and am satisfied, and have done my best here despite all the faults and guilts of being human, then the afterlife can only be a step up. And if I'm good there, I can move up. If I suck there, I just won't progress. I'll stay in that stagnant stage until I find the inspiration to progress. Much like life, even.
A lot of times, also, I feel that this world, with all its aesthetic beauty, has a lot of inherent evil and sadness and other negative things, and sometimes it's hard for me to believe there's something worse. I've been lucky thus far, but living amongst pedophiles and murderers and deadly diseases and chronic diseases and terribly sad emotional and mental diseases... you know I could go on... how is this not hell itself? (Don't get me wrong, I think there are also lots of beautiful things too. But sometimes I can't get past babies being born with diseases and dads raping their daughters, that is, if their mothers didn't drown them during infancy.)
I don't believe in an eternal afterlife. I just don't see how that could be, because if there is an afterlife, it's only our souls that go there. And I don't believe souls ever stop evolving. They don't change from one thing to another, but they grow and adapt based on their experiences. If I don't know anything else in this world, I know that my mind and soul (if they are separate; I'm not sure that they are) continue to evolve with each new experience I encounter. And I can't fathom that would change if there is some new place for my soulmind (I'll just say that, haha) to go when I die.
So for me, I'd rename purgatory to stage 1 of the afterlife, or stage 2 (this being stage 1) of the existence of the "soulmind". How will it be? That depends on this life. If you're "bad", it will be stage 1 of an unpleasant afterlife, to which you can advance into a more pleasant afterlife if you try your best there. If you're "good" here, then, as I said, it will be a step up.