How much memory has your computer got, TTT?
W10 requires at least 2Gb of memory, which rules out many laptops (and quite a few older desktops). However the technical press seem to be reporting that W10 often runs very slowly with 2Gb, and recommend a minimum of 4Gb.
My machines have either 1Gb or 2Gb, so I'm certainly not rushing to get W10. Further, there have been lots of reports of driver problems with W10 (particularly with audio drivers) and I've got some older devices, such as a film scanner and a graphics tablet, that might not have W10 drivers available. (I'm also currently running lots of older software, such as Photoshop 6 and an old version of Microsoft Publisher, in W7's 'compatibility mode'; I'm not sure whether they'd continue running under W10).
So I'm sticking with the maxim of "If it ain't broke, don't fix it!"