One thing I would like to see is the seemless and intuitive integration of plug-ins of various natures similar to those I find in Firefox – not that I use many of them, but I do like NoScript.
Another thing is better integration with some mainstream web sites, such as Yahoo, where occasionally I will still run into page formatting, image display and multimedia integration problems that cause me to copy a page of interest over to Firefox.
A third is Opera's performance on an OS X PowerPC is very clunky, almost as bad as Microsoft Office! 🙂 It would nice to see optimizations to speed performance.
But beyond these, there isn't really anything to complain about. There are features here such as widgets that I played with for about a week and then simply dropped – there was nothing there that I needed. This brings me to my final point. I am afraid that what we seeing here is yet another example of competitive pressures pushing for features that seem sexy but are not necessary and simply add to the software bloat that has crippled far too many programs – Microsoft being particularly prone to this. Everyone wants to stand out from the crowd, and now that the other browsers have caught up with Opera's best single innovation, tabbed browsing, it's getting harder to do so in a worthwhile way. Hopefully, I will be proven wrong. 🙂
As I don't really like chain letters, I won't promulgate this further.