I originally bought mine for an i7 3930K, and I've been using it on my i5 4670K since Haswell first came out. I use it at pretty low RPM's so it's almost silent. I'm happy with it.
It's up there with the best air coolers you can get, right alongside the Noctua NH-D14, and when I bought mine it was a lot cheaper than the Noctua as well. The new NH-D15 might get you a degree C or two lower, but the Noctua and Phanteks are about as good as it gets on air. I think to get significantly better temps you would have to go custom water.
The downside for the Noctua and the Phanteks compare to closed loop water are that they are both huge and pretty heavy. I wouldn't recommend either for a system that will be moved around a lot, like a LAN party box. The NH-D14 and Phanteks also only work with low profile RAM. No tall heat spreaders. I think the NH-D15 is designed to work with tall RAM.