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.
Eh, it's an OK game. I'm enjoying it well enough, but there's nothing about it that's really drawing me into it. I've been too busy to play any games in a couple weeks, and even though I'm only about a quarter of the way through 'Star Trek', there are four or five games that I've been really antsy to get back into a lot more than this one. It's pretty cool to have the entire cast voicing their characters.