Technopeasant I'm the guy that says there's no such thing as first-person 2.5D (certainly not when there's stairs involved) and would call Blood pseudo-3D. To me pinball, cue sports and things like the Oddworld remake are examples of 2.5D games.
And of course heXon! But not the first two installments of GTA.
EDIT: Okay, technically pinball tends to be first-person. But I know what I mean.
Can it get away with 2D physics despite having 3D graphics, and no obstructed view?