It is a fresh install.
I resolved my youtube problems : installed the NPAPI flash plugin, so I have the same config as before, can alt-tab on flash player, but can't have the 60fps on youtube...
For the bookmarks, Sync never worked correctly with me, one computer replaced the other (and I use 3 different...), so I have stopped counting on that.
I can't only copy my old bookmark file, it's a file named "bookmarks.adr", which doesn't even exist in my new fresh install. The whole architecture of the Opera appdata folder seems to have changed.
So the last problem that is really pissing me off is that Opera isn't considered as my default browser and isn't even a choice in the windows default programs.