I kinda like Dante's take on it. If it turns out there is a God and that not believing is a punishable offence, the punishment should be fairly light. A perfect replica of everyday life would be enough for me, as long as I'm aware that I'm not in any shape of control and that this replicated life of mine is under the complete control of various demons.
Past that? I'd make like the Chinese and also a bit like Dante. Ironically fitting punishment depending on the major sin - but in complete understanding of the fact that people are people. Human beings *will* be excessive about one thing or another. It's in our nature. Considering that, if your personal sin is actually not all that significant, I wouldn't make Hell much more than a one-room office, where you meet with a horned and goatee-wearing cloven-hoofed psychiatrist. He just makes you realize where you flubbed, slaps you on the wrist for it, tells you you'll be denied access to a few minor parts of Heaven as penance - and then you're let go.
Say you're an over-eater because you can't process stress. All of Heaven is yours, but your portions in all the restaurants are rigidly controlled. Before long, this will stop being punishment to you. You won't even notice it anymore.
I wouldn't even go so far as to say some people deserve the burning pits of Hell or anything. A lot of the people History has judged to be monsters were just excessively idealistic or misguided - or sometimes just desperate. I wouldn't even torture folks like Ed Gein or Jeffrey Dahmer, because what they do is the result of chemical imbalances in the brain or maltreatment as children. They can't help what they are - why should I punish someone for something they've had no control over?
The most I'd do to these people or to History's worst butchers is show them how they're actually remembered. They haven't succeeded, they're not heroes of the people and they're not celebrated. They've been devolved to common bad guy stereotypes.
Most people die and aren't celebrated. Most of us will die and the world will go on without missing a beat. These people - they're remembered, alright, but not for the reasons they'd like to be. That's punishment enough, I think. Being in the Afterlife and knowing that a lot of people back home actually hate my guts is enough.
I'm pretty sure Hitler figured his name would go down as the man who pulled Germany out of economic despair and founded a world-spanning empire from it. My demons would start by thanking the guy for at least pulling off the first part - only to show him that his Germany started running on the blood and sweat of Poles, Czechs and Jews in general. My guys would show him every single way the concept of Adolf Hitler as a character became an object of scorn or comically gleeful evil. I'd show him how long it took for things like Bruno Hirschbiegel's "Downfall" to pop out of the woodwork, because the living aren't comfortable with remembering Adolf Hitler as a man. It's easier to think he was this big, grinning cartoon boogieman you can spit at or crush with a Tom & Jerry mallet than it is to consider that he had his quieter moments - that some people could count him as a friend.
To me, unless the guy is still caught up in his own hubris so long after blowing his brains out, this would be punishment enough. He'd be let into Heaven, but as my Heaven is an exact duplicate of mortal life minus all the inconveniences, he'd regularly be confronted to video game Nazis and their Dieselpunk occultists, to Tex Avery's wolf and Charlie Chaplin pulling off exaggerated versions of his salute, to Rob Zombie's cartoon Nazis in "El Superbeasto" - and everything else ever to have made fun of the Waffen-SS.
I'd even let him see how his uniform iconography is remembered. A lot of people find the SS uniform to be badass or appealing, but the guy would realize it isn't because of his contribution to History. A lifetime's work, and you're rewarded by seeing your best troops' uniform being worn by horny couples looking for softcore BDSM.
That *really* is punishment enough.