Is that any good and worth to install it? I have a lovely Windows 7...
Depends. It should be way better than 8 and it's free for like half a year from this release for 7 & 8 users. The thing do you benefit too much (for gaming performance) from upgrading lies behind your rig. DX12 will boost at least AMD multicoreprocessors like 30%:
http://www.winbeta.org/news/amd-directx-12-will-finally-unlock-true-potential-your-multi-core-cpuSome i5 performance with win10:
https://www.youtube.com/watch?v=XzFe5OOHZkoedit: anyways I'll wait at least for 1 week for results from new win10 users before moving into it safely. At least you should be able to make win10 interface look pretty much like 7 (it was possible with 8 aswell with some tweaking). Not more of that, haven't really orientated in win10s new features.