OSR/D&D: Single class parties
Ohh, you mean like Avatar: The Last Airbender but without magic, or Gears of War without the aliens, or the Power Rangers without giant transforming mecha, or...
Okay, I'll stop. Honestly, it's a fine thing to do so long as people are willing to differentiate their characters in ways that aren't always going to be backed up by mechanics. Maybe they've all got Strength 20, but one is a bodybuilder and another is just incredibly fit despite his size. Maybe they all took Improved Dodge (or whathave you) but one girl flavors it as being nimbler and the other attributes it to some flashy/distracting swordplay. And, of course, there can be plenty of mechanical differences, but you've mostly just gotta get a group of folks who don't think that a character's class is their most defining trait, and then a subgroup within that group of people who don't mind having fairly similar builds (especially at the beginning of the game).
I like to think of these games as the ones that explore every shade of blue, instead of every color of the rainbow. They can be amazing with the right group of people (which you kinda need from the outset, as I just said), and they certainly gave me new perspectives into just how diverse people with the same numbers can be.
Hope that helps.