1.) Whenever you right click on something and click "Open in a new tab", half of the items you do this with opens the new tab, but it doesn't load the page. Sometimes you need to do it 3 times before it actually loads the page, and there is nothing being done differently than any other attempt.
It just looks like Opera is waiting for "pipes" (max multiple connections cap) or availability of the computer resources to the renderer. It ends up loading.
2.) Saving images to your computer. Previous Opera versions allowed you to save a picture, simply by right click, save image. With Opera 23, that feature is gone.
What!? It's there. o.o
3.) When installing Opera 23, it doesn't ask if you want to uninstall older versions... "Dumber" users may not realise this, and then sit with several Opera versions on their PC
It already uninstalls all versions. It shouldn't even list multiple versions in your computer. If you're talking about Opera 12 it's a different product altogether though.
4.) Opera Software ASA, seriously, saved sessions? You remember that feature? PLEASE BRING IT BACK.
Yes, right-click the tab bar and select Save tabs as Speed Dial folder. When you want to open it right-click the folder. Much better to organize the saved session than the old way. When bookmarks are back in full in a future version you can use a bookmark folder but the thumbnails makes recognizing the pages so easier that I don't see myself using a favicon+title list anytime soon - let alone only a name that will open all the saved pages at the same time without you remembering exactly which ones you had saved and without an easy way to edit the session.