I loved the first W10 consumer preview, but soon after that they stuffed it. If it wasn't for the compulsory updates that you can't turn off, and the slow folder opening - that stupid green bar scan -, it's good enough if annoying. Basically my i7 960 with W10(SSD) feels touch slower than W7(SSD) on my E8650 Core2Duo.
No one says you have to upgrade to W10 when W7 stops - if I didn't get W7 for $10 I would still be on XP -, and in fact you can still see XP in many commercial installations. I'm going to keep W7 on my high production i7 4770(SSD) because it's very responsive.
You can still update W7 to W10 free, but put in on another drive so you can go back. From memory I drive imaged W7 to another SSD and updated that. I will probably never use the W10, but it is only a cable swap away if I have to.