The only real issues I've had with it are the silly way they make some apps (like the XBox one) harder to remove, and the blatant amount of spying it does (for example, by default, it phones home to MS with every single keystroke and mouse click, so all your login credentials for everything, including things like online banking, are compromised). It's certainly worth investigating the privacy issues involved before you upgrade. In their defence, they now present you with pages of settings that you can disable during the install process - initially, the settings were all over the place and you had to know where to find them. Still, it's kinda like asking the NSA to be your internet provider and I can't say I entirely trust that there's not other spyware still to be discovered.
As far as gaming goes, I've had zero problems; in fact, a couple of games that were having issues under windows 7 work flawlessy under 10.
Personally, I've run an app that claims to disable all the spyware and I log in to anything sensitive on a linux PC or using RSA keys. Not an option for everyone, sadly.