I'm amazed at how many people don't "get" this.
60fps will produce a cleaner image than 30fps, and will on average decrease response time. If everything else stayed the same and the game wasn't locked at 30fps for artistic reasons, 60fps would always be better. It's no different than a higher render resolution, larger textures, better AA, longer draw distances, etc. Each one makes a cleaner image and ever so slightly can help with gameplay.
This is a great website that allows you to try out different framerates for yourself: http://frames-per-second.appspot.com/ Not perfect of course, but imo it does a much better job showing the difference between 30 fps and 60 fps than side by side gameplay gifs.
As you can see, a higher framerate is BETTER!
But... it's hardly ever worth it.
Resolution, special effects, etc. are far more important visually. Gameplay wise, resolution and draw distance are more important as well. It's incredibly silly hearing people say 60fps games are much better to play than 30fps ones. A frame in a 30fps game is only on screen for 33 milliseconds. A frame in a 60fps game is only on screen for 17 milliseconds. Thus the difference is 17 milliseconds. That sounds like a lot when monitors are advertised with 3ms response times, but it's actually pretty short. It's nothing compared to the amount of time it takes from pressing a button to seeing a resulting pixel on a TV screen.
I mean just switching to a low latency tv and a low latency next gen controller will shave off way more than 17 milliseconds from the game's response time.
We will never see a generation where 60fps is the standard, and that's a good thing.