It's a love story for the ages: two of most important names in PC gaming history have finally admitted their feelings for each other, and after a whirlwind romance they have a beautiful bouncing baby. Yes, Doom and Diablo now have a child to call their own, and of course it's as gloriously moronic as its parents.
Doom: Fall of Mars is id's setting, monsters and essential armoury dressed, with surprising finesse, in Diablo's clicky clothes. It is cheerfully shameless about it, employing the sprites et al of Doom, and the oh-so-familiar fonts and inventory of Blizzard's kill'n'collect pseudo-RPG. While this is only a proof of concept demo (comprising three levels, a few bosses and a ton of what I believe the younglings call Phat Lewt), it's safe to say it realises the cartoonishly compulsive elements of both games remarkably well: this is a standalone modlet that we gladly award the official RPS A Right Old Giggle trophy to.
It's also a mere 3.3Mb, and you can snag it from here. Oh, and the guy behind it calls himself If Software, which is about as apt a studio name as there could be for this wee retro genre-bender.