Theres no denying this is vast improvement over the previous versions. I'm currently running the 64bit version and have had NO compatability issues as yet and I have noticed an impressive speed increase on both start up, shut down and generally running applications and performing actions.
Obviously it looks nicer too, but thats a given.
One thing you need to realise is that when installing Windows7, it will default your display to VGA. If you are running your monitor using a digital connection the screen will go black.
This happened to me, and I was worried it was messing up. I changed my connection to VGA and realised it was waiting for input.
Bottom line... I would recommend this, especially on 64bit.