If your game’s target platform is mobile and happens to be aimed towards males 18-30, you definitely want to hit toucharcade.com’s forums. If it’s aimed at a more general audience/casual one-button, my bet is it won’t get much hype on there, but who knows! Look at geometry dash!
Also, there’s a thread somewhere on here holding a list of reviewing websites. I’m going on a quest to find it and I’ll edit once I do.
edit:
Ok, so it’s super out of date, but perhaps there are still some relevant infos on it.
Those are not exactly websites that allow you to expose your content freely, but they can help with visibility if you make an inviting press kit.
Just in case you haven’t seen it yet, Unity has their Made with Unity section of the website. Have to imagine though that most of the people who use it on a regular basis are other developers which doesn’t really help you a whole lot.
Outside of this my advice would be to get some cheap hosting and create a dedicated page for the game, and then go to the areas of the web where your target audience exists and advertise/discuss the game with them.