1. It will have better graphics, but cost more than the 360 and the Wii put together. That is because its going to play Blueray.
2. The 360 does NOT have backwards compatability. Not genuinly anyway. For 90% of games you have to go online to
www.xbox.com and download something so that they can be played on the 360. There are a ton of games that still are not available, and there are a few (Like Halo 2) that will work right away. Over time they hope to convert all Xbox games to be 360 compatible, but you still have to download that crap.
3. Yes. They also revamped the graphics on Halo and Halo 2 specifically for people playing on a 360 and they made it look a little better.
I have a 360, its great, I love halo so its a must, but to be honest they pushed its release date at the cost of quality, and now you as a consumer are looking at a product that is probably 98% finished. That 2% isnt that big a deal, but things like not having true high definition and backwards compatability are what should sway people to the PS3. Not that they cant screw up either, they just havent yet.