If i buy game on GOG can i play it now, or is just preorder and i have to wait for relase day?

You can play the 'in dev', incomplete version that everyone on this forum is playing. If you read through the forum you can learn what they have experienced. Then, on release day (not for a year yet?) you will be able to play the complete version.

the final game is at least a year away... prob more like 2
you get the work in progress reguardless of what platform and they track your game play to help work out what to fix... like the bonus from high ground

You can "play" it, but not really. You'll find differing accounts from different people, mostly depending on how hard they are fanboying about the game, but the "early access" aspect of this game is less early access and more late alpha. Game's still riddled with bugs, glitches and errors that should have been ironed out well before a beta, much more so for an "early access". Also a ton of content is just straight up not there, which is scary since they claim the game is going to be particularly large. You can go through most of chapter 1, and that's it, and you can do it with only about half of the classes and races D&D, and you can't play as any of the 5 story characters in the game. And there really are only three main areas (4 if you count this new area they put in with the Sorc update), so you'll very quickly bore through the amount of content that is there.

And to just kinda cement to you why that's all a problem, Patch 6 was released about 2 weeks ago. 3 days ago they released hotfix 16 to address a bunch of crashes, errors and bugs that it caused. And today they released hotfix 17 to address crashes that hotfix 16 caused. And now it crashes anytime you complete the prologue, so you can really only play the prologue over and over again until they fix this. And this is about the 12th time they have caused this particular crash with a hotfix or patch that I know of.

If I were you, I would wait for the full release to buy the game. It is not worth it right now, and it's not smart to support companies doing this early access thing if it's going to be this bad or predatory. I just installed it again after about 9 months without bothering with it to check out the new content they added, and I can't get past the stupid prologue crash, so I've uninstalled again and waiting for the full release. I advise you to do the same.