Opera 8’s UI really had most everything it needed to be a great browser (I haven’t upgraded at work and can barely tell the difference). 9’s big delivery is in the area of web standards (opacity, SVG, DOM Style) and hot proprietary ones like rich text editing, Flash-Javascript communication and the Canvas element. There are additions to write home about on the UI side as well (site-specific settings, content blocking), but the under-the-hood stuff above is what will truly allow a new Opera user to use the latest web sites they’re already used to without getting a broken/dumbed down interface or being flat out blocked.
The new widgets feature is surely meant as an answer to (or at least a distraction from) Firefox Extensions, but I think this move will only make it more apparent that people really want to customize their browsing experience rather than collect desktop gizmos. Even with all the headaches associated with dealing with managing Extensions (and upgrades)–and I’ve dealt with them from the Mozilla 0.9 days through Pheonix and now Firefox)–the modifications they can perform are staggering and impossible to ignore. Although extensions give you the power to wreck/destabilize your browser and make upgrading a pain, users now expect that power.
A couple things I’d personally like to see in Opera is a richer panel implementation and maybe some advanced Javascript extensions. Mozilla/Netscape7’s “sidebar” could’ve used a better control UI, but it allowed multiple panels to be visible simultaneously. I think if Opera encouraged web developers to develop panels with the same gusto as they promote widgets, they might prove more useful just because they live inside the browser where the user lives most of the time anyway! Maybe I need to create a slick panel as a proof of concept. In the Javascript area I’m thinking some extra interfaces available to bookmarklets (better persistant storage than document.cookie, local storage of JS libraries) could help make up for the lack of extensions. Just some ideas…