First impressions - good!
Ive just installed Fedora 20 and its looking good. (Default image - Gnome 3.)
No problems so far, though the CSD for none gnome apps looks a little weird.
Aesthetically it seems that for large monitors gnome enters into the uncanny valley of good looking - almost there, but not quite.
(With recent changes in rendering I think Gnome can now also have proper transparency in windows instead of faking it... would be interesting if some glass themes are not created)
I did the usual, install from lice-cd, installed adobe flash repo and rpmfusion. (I rarely watch anything on DVD so I am not sure how necessary libdvdcss from livna is any longer...)
I would have done an upgrade but this coincided with getting a semi-new PC. Dual boot works fine. Radeon HD 6870 works fine.
In a month's time I will probably be able to play Total War on linux, so I will wait til then to install steam.
The new gnome software centre is really good - even though not all apps are listed - I failed to find corebird in there and had to revert to using yum
Looking at Koji, it seems that Mesa 10 is Fedora 21 territory.