There are a lot of sites that hate Opera...Words With Friends on Facebook ("...we have discontinued support for Opera XX"), for one, and tbs.com for another (won't play videos).
Too bad...Opera's one of the best browsers that you can still tweak to your heart's content (unlike many others, such as Chrome (disabled "non-Play Store apps"), or Internet Exploder (worst broswer ever)).
Opera's not going anywhere, so the site owners that refuse to work for Opera better pull their heads out of their @$$es and get with the program.