Takei was unique because he had that distinct voice. a friend of mine heard a clip of him on the radio doing something for Howard Stern or whatever and asked "is that the Sulu guy?". he just has that extra little presence that Cho just didn't have with the whole voice thing. what is that, baritone or something? Nimoy had it for Spock but Quinto didn't and that was just as missed
Agreed. I think that's one of the things that the new movie didn't really take into consideration. Takei, Nimoy, & DeForest Kelley all have pretty distinct voices which Cho & Quinto do not have. And while Karl Urban came closest to imitating his predecessor, it seems a bit off because Urban is using affectation to try to resemble the lest affected member of the original cast. Urban is trying really hard to do something that Kelley did with absolutely zero effort.
For that matter, other than both being Asian, I don't think Cho looks at all like Takei. Takei has a very round face while Cho's is much more angular. (And Daniel Dae Kim would have presented the same problem moreso.)
But overall, it doesn't really matter. While he got to be in a pretty cool action set piece in the new film, his character was such a cypher on the original series that it kinda didn't matter who played him.