I have to disagree, I am writing this comment on the latest build (10122) of the Windows 10 preview and as a Windows 7 user am very impressed with it. Back in January I was not very enthusiastic about Windows 10 but since the preview was free I would give it a try and was pleasantly surprised. I loaded it onto a fresh partition on a Lenovo Laptop which took ages to boot and crawled under Windows 7 Professional. It has rejuvenated the laptop! boots in about 40 seconds and is much, much faster in use. I loaded up some old games(Quake 2, Quake 3 Arena) and they run better than on my desktop Win 7 PC, compatiibility updating seems much improved. All my usual apps run perfectly - Firefox, Thunderbird, LibreOffice, VLC, Irfanview, etc. I have actually grown to like the start menu and the tile apps - news, finance, food, sport, video, photos, etc. As someone who never upgraded to Win 8/8.1 as I really was put off the interface, I now am using Win 10 preview in preference to my Quad core SSD Win 7 PC.
There are still a few bugs and it is a bit rough around the edges but it is stable and no show stoppers.
I for one will certainly looking forward to updating my main PC to the release version.