Not necessarily, you could have done much of what was done in Mass Effect with the existing characters. Talk to Sulu, Checov, Uhura, and so on about their respective pasts and give them missions. This is, however, a much more linear game than Mass Effect, though. Linear doesn't necessarily mean bad, though. I will say, ME is about what I want from Star Trek. It's also, amusingly, pretty close to JJ Abrams movies with better plotting.