I don't know if I'm in the minority here or not, but I really didn't care for Firefight much. At least not in Reach. It was cool as a survival/fort protection type game in ODST, but it was too arcade-y in Reach for my tastes.
I actually like Spartan Ops. As was said, it is short for the most part, unless played on Legendary alone at least, but it ties into the main story well enough, and I like the objective based design. All they need to do is make the stages a bit longer, and give us more diverse locations in future episodes and it'll be fine.
I'm sure with feedback 343i will make it even better in time.