1987's Street Fighter was a pretty well-received game in its time, even getting ports to numerous home computers and even the Turbografx-CD, but is generally ridiculed nowadays for its stiff controls, choppy action and absolutely horrendous balance. Even Capcom barely acknowledges it these days, other than including it on a token digital compilation or the odd reference in in-game lore. Still, the game does retain a small following; enough of one to get a full remake in the MUGEN engine. Street Fighter One adds numerous improvements from later entries - smoother gameplay, combos, super moves and, of course, being able to play as more characters than just Ken and Ryu. They even added in a bonus character in the form of Cody from Final Fight. So if you want to see a largely-abandoned first entry in a legendary series get a new lease on life, it's one to give a try.
