People saying Vader was fan service in RO: wasn’t he originally supposed to have all of Tarkin’s scenes before they gave the go-ahead for the CGI? I think he originally had a much larger role.
Plus, I think he fit just fine in the film. I actually think, unlike the ST, RO gets better with each viewing.
His appearance in itself wouldn’t be fan service if he did something of value to the plot. Mon Mothma and Jimmy Smits weren’t fan service. They had a tangible purpose in the film. I’d have much preferred Vader to the cartoon Tarkin though. His lightsaber battle actually might have been better had he been built up in the film itself and not just thrown in there under the assumption that he’s the most badassest villain in the galaxy.