Level Up is based largely on original 5e with a number of additions, and feels different from 5.5, and certainly different from either version of PF, at least in my opinion. More simulation-focused than either game I think, with more depth than either version of WotC 5e and less hard focus on gamism over setting logic logic than PF2 from what I've read and heard of it. Haven't seen much of Starfinder so can't really speak to it
