Action RPGs - games that offer nothing but fast, real-time combat. You kill monsters, collect items, level up, kill bigger and badder monsters, collect better loot. Rinse and repeat. Nothing distracts you from killing, looting, and levelling. Silly things like story and characters won't get in the way of your action. Choices mean "which item compliments this build more". The goal is to make an ultimate killing machine in the chosen class, capable of cutting through anything the game throws at you like a hot knife through butter, achieving the prized "IT'S OVER NINE THOUSAND!" power status.
Contrary to popular beliefs, the concept of killing things in real-time as the main attraction isn't a novelty, but a 25-year old veteran. Two biggest events are Gauntlet, an arcade 1985 game, and Diablo, a 1996 game that started the clone war mentioned in Star Wars. Condor Games pitched the idea of "Gauntlet with better graphics" to Blizzard and although the idea was laughable, Blizzard decided to give this craziness a shot, bought Condor and renamed it into Blizzard North. The idea was laughable because in 1992-96 huge behemoths like Darklands, Star Trail, and Daggerfall ruled the RPG world offering so much more to players. Ironically, the dinosaurs died, sticking with the the evolution program, and were replaced by waves of Diablo clones: Nox, Darkstone, Revenant, Lionheart, Space Hack, Harbinger, Blade & Sword, an army of Dungeon Siege games, Sacred, Fate, Loki, Silverfall, Restricted Area, Gauntlet: Seven Sorrows, Titan Quest, that outstandingly horrible MageKnight game, Space Siege, Rise of the Argonauts, Mythos, and circle-completing Hellgate.
Diablo 2 still remains the king of the genre, offering brilliant and unmatched design.