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.
I've just checked F20 on Dell vostro 3500, Intel(R) Core(TM) i3 CPU M 350 (ironlake?). No tearing at all.