I have thought for a while that the 4E game system is actually better suited to the XCrawl setting than 3.x, which it was originally published for.
For those of you unfamiliar, the following is a brief description of XCrawl:
Take a pseudohistorical D&D world, and then advance it to something very similar to 1980. The equivalent of the US is a Roman-style North American Empire, as the use of magical communications and similar allowed the Roman Empire to persist much longer than it did in the real world. There is substantial modern technology, but not quite the same as our Earth; the presence of magic and powerful deities has distorted technological progress. Some things are simply much easier to do with magic than they are with technology, other areas of technical advancement have simply had their course changed.
There is drastic social inequality on a number of axes, both between the races and between the various strata of society, as Aristocrats have distinctly more legal rights and privileges than the peasantry. The underdark is like a ghetto where the orcs and so forth have to live. There are still wild unsettled areas right in the middle of civilized nations, because things like Great Red Wyrms are entirely capable of making life inconvenient for modern military forces.
One day, some archaeologists uncovered an ancient intelligent magical sword, which had spent a century or two adventuring along with an Elven bard. It told them tons of fun stories about, basically, D&D-style adventures it had been on, and they published them. This caught the public's imagination like Harry Potter and The Da Vinci Code combined.
In a handy coicidence, Emperor Ronald Reagan needed something with which to distract the populace from how thoroughly they were being screwed by the existing social order, so they invented XCrawl: A gladiatorial game show based on ancient historical dungeon crawling. If you've ever felt that old-school dungeons had a bit of the demented game show about them, it's now explicit. Adventurers with modern reproductions of armor and medieval weapons (in some cases covered in logos like a stock car) bash their way through mazes constructed and run by celebrity Dungeon Judges, with the challenges and conduct of the Judge and the party being ruled over by neutral referees. There are deadly traps, monsters that have been trained, magically dominated, or simply hired in the case of intelligent ones. There are "princesses" to rescue (bikini models in entirely mock peril) and wild treasures (piles of gold, a jet-ski, a year's supply of car wax...) plus glory and fame and an escape from drudgery.
I think this could be a hoot, given a GM and some players. The PCs are combination movie and sports stars, the games tend to foster intense rivalries between different adventuring groups, there can be deep tension between the referees, the arena staff, the DJs...and adventuring parties and DJs ahve been known to hold grudges against each other, as well. There's plenty of fodder here for adventuring, combat, and adult entanglements of various kinds.