Anything in the Temp directory can be deleted, they are temp files. However many of them are likely being actively used so some you may not be able to delete. Furthermore some files may contain logs of setups that could be useful for debugging installation issues. But in general anything in the temp (yours or Windows) can be removed.
A quick google indicates that Opera may generate these temp directories. You might be able to look inside them to see if you can tell but deleting them should be fine. Properly built apps should clean up their temp files anyway.