Yes, new races and classes would be good.
No, new races and classes wouldn't be good.
I don't mind either way.
To keep the game interesting and more replayable I think that over time new races and classes should be added over time. With only 3 classes and 3 races at the moment the replay value would probably be less if these were the only ones throughout the game's lifespan. With new races and new classes this would add a greater in-game diversity and keep gameplay fresh for both the campaign missions and the Crucible. I do realise that Bungie may add more races and classes over the game's lifespan but I'm just voicing my concern to the possibility that they may not. I've added a poll to see how much or how little people agree with this.