Hmm. Well, can't try out the character builder yet.
The monster/item/spell reference is already loads better than 4E's DDI Compendium... literally loads, as in it loads instantly. Might benefit from some more sophisticated filter/search tools, especially as more content gets released, but it's solid just as is (and I know from personal experience what a pain in the neck it is to build good search tools).
The magic item editor looks really spiffy. Can't wait to play with homebrew items on a working character sheet.
Spell editor is equally spiffy. I'm assuming it will give you the option to use those "modifiers" for stuff like auto-rolling damage? Again, need a working character sheet to see this in its full glory, but I like what I'm looking at.
The monster editor is... not so spiffy. Oh, it gets the job done, but it doesn't seem to autocalculate anything. It doesn't even do the very simple stuff like computing average hit points, let alone the complex math that goes into estimating CR (granted, there's no way you can fully automate CR, but you could allow the DM to estimate damage values and other modifiers on the monster's abilities, then calculate CR off that). This will need to improve significantly for me to want to use it.
The campaign editor is little more than a placeholder. From the announcement, it sounds like they're aware of that and it's on the roadmap, so no complaints there.
All in all, assuming the character builder is solid, I like what I'm seeing. It's nowhere near finished yet, but an excellent start.