I'm sure they won't detract from the original game's plot or pacing. Worst case scenario is new enemies and easter eggs off to the side I'd say.
And one more thing - I don't have a 360, so I've never played any of the other games besides Halo CE. However, that does not stop me from enjoying the well crafted universe. Halopedia has been a great friend for letting me follow what is going on in the world of John 117. ;)