I don't think those ads are remotely intrusive, but I'm concerned about Microsoft's ability to sell the ad-space. If this doesn't work, they may scrap it and replace it with something a lot less palatable, like a fixed ad window in the lower left corner.
The in-house ads that they had before were click-to-play game trailers and direct response ads of the "buy now on XBLA and get 50% off game ABC" type. These are ads that require very little time to grab a response from a consumer. Even if a user was just flipping past the tabs, there's a good chance that they'll see the entire ad, and they may stop to look more closely or respond to it.
A 15 to 30 sec video/audio ad, however, actually requires users to stop and look at the ad for an extended period of time for the pay-off. If I'm an advertiser, and I know that the vast majority of users won't see more than a second of my ad, Microsoft is going to really have to lowball it to sell me the ad space.
It all comes down to the numbers of course, and maybe Microsoft has already sold the ad space to movie and TV studios to show trailers that people might actually want to see, so they believe that their actuals will match their predicted numbers.
But I'm skeptical it will work, and if it doesn't, I think there's no way MS won't try for something that's less easily dismissed.