I'm currently using Opera browsers on both Mac and Linux (Ubuntu) machines. The "close tab" button on my Mac is on the left hand side of the tab, while on my Linux machine it's on the right hand side. It's very annoying because the position of this button should really be consistent across different platforms.
It would even be better if there is a switch to let users decide which side the "close tab" button should be placed. I personally prefer it to be on the right hand side of the tab, similar to that on Chrome and Firefox.
Otherwise, I'm satisfied with my overall Opera experience