First impressions? Well:
I love the fact that they used a rendition of the "Finish the Fight" track from the HALO 3 soundtrack. That is one of the very best tracks from the very best soundtrack of the very best game in the very best FPS series ever made.
The graphics look pretty amazing - but not quite as photo-realistic as they should be, given current technology. HALO 5: Guardians had better overall graphics even straight out of the trailers. Of course, this is just an announcement trailer, not a serious gameplay video, so that is to be expected.
The news that I am seeing concerning HALO Infinite's gameplay is extremely encouraging: