Small thoughts in no particular order:
- The chrome changes are subtle but cool- they take an already beautiful OS another step forward.
- Mission Control is an evolution of Spaces and Expose.
- Fullscreen apps are executed beautifully. If you launch one, it becomes its own Space. If you close it, it disappears. Move your mouse to the top of the screen, and the menu bar (and bookmarks bar in Safari) reappears. I'll probably use this feature quite a bit.
- New gestures are cool and intuitive. Pinch in with three or four fingers and a thumb, and you get Mission Control. Pinch out, and you see your desktop.
- Launchpad feels like an iPad, but it's kind of pointless if you're comfortable with a filesystem (or you use Spotlight, Quicksilver, or another launcher). Reminds me of the silly expanding Application folder from 10.6.
- Overall, there's lots of UI abstraction all around. If you can use a phone, you can do almost anything, from installing apps to saving and finding files. Default finder window view is "all my stuff," sorted by type and date. This will be big for kids, the older generation, and new computer users.
- When you install, it creates a restore partition on your hard drive: you can reinstall the entire OS at any time, no CD or target disk mode required.
- Most exciting features for normal users: AirDrop (wish it worked over thunderbolt), fullscreen apps, maybe Versions and autosave.
- Most exciting features for techies: full-disk Filevault, multiple sign-on (via remote desktop).
- Coolest surprise: digital signatures in Preview. "Hold your signature up to an iSight or FaceTime camera, and Preview uses sophisticated image processing to turn it into a pen-perfect signature annotation. With a click, the signature is added to your document, which can be saved or sent via email. It’s ideal for signing PDF forms and documents."
Full list of features here. Fun stuff.