DailyGamerBlog.com recently did some video impressions on the new mythic map pack levels for Halo 3.
"So it all comes down to one thing. Is the Mythic Map Pack worth it? Absolutely. This is one of the best map packs Bungie has ever put out there for the Halo franchise. If you are into Halo Wars, go get the Limited Edition. If you aren't, get it this Spring on the marketplace."
Sounds like the new maps will be great.