To be honest, my reaction was 'meh' as well. While the idea of another Halo seems tempting, what will this Halo have that we haven't already seen? It will have to be a fresh fruit, because the whole covernant thing is getting kind of tedious. They were awesome in the beginning, possibly some of the most interesting and original aliens and enemies in gaming, but now they are becoming rather annoying, I want a more serious threat, something more destructive and with more evil intent, an army of these things occupying a part of space and ready to create chaos.
Gameplay could do with a refresh as well, especially if they are doing another trilogy of this series. Bungie will remain in my heart for making some of the best games I have ever played, what Microsoft has to show without Bungie is another question in itself.
I personally don't think Halo will have the novelty that Bungie made great anymore.