I'm not sure this is unpopular, but I absolutely hate the "V" on the foreheads of TNG Romulans. It was a damn plot point in "Balance of Terror" that the Romulans looked just like Vulcans, and with that big "V" on their foreheads they look no more like Vulcans than whatever forehead alien of the week looks like Humans.
I think that's actually the popular opinion. I certainly agree.
I should also add that I'm not crazy about Q, and that I think season 2 of DS9 is great and better than season 3, possibly season 7 as well. I don't know if it's that unpopular of an opinion, but many people like to repeat the mantra "season 3 is when the show gets good".