One of the reasons why the new Opera is my secondary browser - it's not good for someone who have to do a research and opens dozens of documents every day and chooses to save only a few of them. For that purpose Opera's current way of handling downloads is time killer and (very) annoying at best.
It is a design decision based on the fact that everyone have enormous amounts of storage space available. You can clean up your Downloads folder once in a while instead of having to decide between saving and opening files.
The old Open button in legacy Opera’s Download dialog but files in a cache folder instead of the Downloads folder. This confused the heck of many who could not find where their files were stored (because either option would store the downloaded file on the system).
The new way is easier to use because the same thing always happen when you download a file. But some control of individual files is taken away to achieve this.
It is a simplification of a regular task that did not need to be as complicated as it was.
That is coming off a Opera dev. I find it kind of insulting, frankly