While Macromedia's interfaces have always taken a back seat when compared to Adobe's, I have to say the redesign Macromedia has done to it's new lines is a major step up. I love the new pallettes, which are similar to Painter's collapsable pallettes. Also, all of Macromedia's apps now features the Properties bar, ala Dreamweaver. This bar can handle many context sensitive tasks (fonts, keyframes, movie settings, etc.) all from one centalized pallette.
flash MX's new tools are just simply stunning. What took a ton of Actionscripting knowledge to pull of in Flash5 can now be done with reuseable widgets in MX. Makes creating Flash web applications much easier.
LiveMotion2 has some real nice features too, but scripting still isn't one of them. While it finally does have scripting, it isn't nearly as complete as FlashMX. Plus, it isn't as well documented, making learning it a bit tougher as well.
As for performance, the beta I tried a few weeks ago had pretty good performance on my G4/800DP. Don't know how well it fares on slower Macs though.