Halo doesn't scare Nintendo at all - but it may scare Sony. Launching it before GTA is a masterstroke - gamers will pick up Halo in September, then grab GTA for their shiny new 360 in October.
If MS wanted to really run this all in - then release a killer app (?) for Thanksgiving - along with a price cut.
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Here is a question for you all - which will sell more hardware - Halo3 ... or a combination of Wii Music & Wii Health pack...?
Its going to be a huge, savage end to this year. I think Sony will be happy to concede the US to MS - and focus on next year.
EDIT - Ninty sees Sony as much more of a threat than MS. The stronger MS get, the more this hurts Sony - and this isn't something Ninty minds that much at all...