That's very cool, but I generally like Reach's normal intro more. Tunavi's makes for a more exciting hook, but you have to remember that it's still a video game - you can't just drop unfamiliar players into an intense firefight right at the start, you have to give them the slower tutorial section first.
I like the pacing at the very beginning of Winter Contingency - I just hate how the reveal of the Covenant is spoiled so quickly. I would rather fight Insurrectionists (easy human opponents) for most of the level, all the way up to the actual Visegrad relay. Then, once you're about to squash the Innies that are trashing the relay, the Covenant shows up and surprises the hell out of both groups.
And the reveal shouldn't be you chasing a lone Skirmisher, it should be an Elite that drops in through the roof on top of you while you were distracted by humans.