There are a few conspiracy theories and a bit of confusion about MS giving away free Win 10 upgrades.
Basically,
- it is free,
- it works well,
- it is a vehicle for MS to sell you stuff (although how intrusive this is remains to be seen).
- it does have some dodgy privacy settings, but you can turn them off.
It looks like MS is shifting it’s revenue model. It apparently makes very little on upgrades so it is giving away a system that will make it easier for you to buy related MS services and apps
http://www.zdnet.com/article/microsofts-windows-monetization-plan-services-are-the-new-attach/
It looks like a good system, but the upgrade process has been problematic for some people.
http://www.windowscentral.com/errors-windows-10-upgrade-fix
Here is a collection of reviews (very positive)
http://www.engadget.com/products/microsoft/windows/10/
There are some dodgy default privacy setting, but you can configure them
http://bgr.com/2015/07/31/windows-10-upgrade-spying-how-to-opt-out/
Should you upgrade? PC Adviser says ‘yes’.
The OS is clean, familiar, and easy to understand, plus it has a wealth of new, helpful features that you’ll actually want to use. The fact that it’s free for the majority of existing Windows users, and can be rolled back quickly to the previous version if you don’t like it, really makes it very, very easy to recommend.
http://www.pcadvisor.co.uk/feature/windows/should-i-upgrade-windows-10-advice-better-3618139/
Personally, I’d wait until the next update in October. The truism when dealing with MS is “never get version 1”.