User experience matters a lot to me. I have tried, tweaked, installed, removed, loved and hated many desktop environments in the past.
My favorites among them are KDE and XFCE for reasons, too complex to discuss here. But, they all had one thing in common: the way they feel and behave by default (on most distros) does not compliment the way I like to operate a computer. Thus I always found myself applying changes of various extend until I felt "at home".
About one month ago, I booted into a live session of elementary OS Freya Beta 1. I did this just out of curiosity and without any serious expectations. Having seen screenshots before, I had an idea of how elementary OS looks, but that's not the whole story. The whole OS is crafted with many aesthetic details that go far beyond "shipping with a nice GTK theme". It is hard to describe and highly subjective, but as I perceive it, it feels great to interact with every part of the system.
The design of the user interface is alltogether simple and elegant, with very little room for customization. That may not be everyone's cup of tea. Customization has it's value. Infact, there was a time, that I thought it would be smart for an email client to contain 10 pages of settings. I'd even say that the ability to tweak everything was one of my major motivations to switch to open source software in the first place.
I've learned my lesson: If the default settings are well-wrought, there's no need to configure every detail. This applies at least for what I call "everyday applications" i.e. email client, PIM, file manager, browser, etc. I still consider it preferable to equip professional tools, like IDEs, CAD software or multimedia production suites, with many options and utilities, because it is of actual use in such an environment.
If you would have liked to see benchmark results here, I have to apologize. I do not consider numbers a reasonable measurement for "user experience".
During the last month on a Beta release, I have experienced uptimes of more than 5 days without lags, screen freezes or desktop crashes. In contrast, while testing Gnome Shell and Cinnamon I experienced stuttering animations and delays before switching from one workspace to another, especially with many windows open. In my opinion that is a deal breaker, as I find these delays very distracting.
On my machine, elmentary's desktop shell Pantheon and its window manager Gala have performed as good as lightweight desktops like XFCE, which impressed me a lot!
After using elementary OS daily for about a month, I plan to continue using it for my professional needs, because, out of all the computer environments I've had my hands on, elementary offers the most pleasant user experience and for me, it "just works".
That being said I may as well switch to something else out of curiosity or boredom one day, but at least I cannot see any rational reasons to do so at this point :-)