The style of gameplay, which is "Souls-like", a particularly player-antagonistic form of gameplay. Named after the first most popular entries in the line "Demon's Souls" and "Dark Souls". You really have to have an almost masochistic streak to enjoy them.
The other category is the design aesthetic. Kind of an industrial, Victorian, steampunk look and feel. Fortunately there are way, WAY more accessible games with a similar look: