I see alot of negative input, but more specifically, i only care for not just the campaign but outside that like survival and infinite warfare survival so to say. Seen this on steam for 19.99 and wanted to buy on gog, is it worth the buy, if i don't care for the campaign?

Does it support player modding?

Steam version support some modding. And Workshop content - best of what you can get from *game*.

Survival is worse than campaign. Campaign is good, but have so simple (and that mean most fru-u-u) bad things. Soldiers on hero missions only for few (of 10 total missions). No hero for Horde survival and main missions. No abilities for hero except grenades pick-up. No research tree reset (pick wood stones and later in campaign stone walls instead or something like that).
Some minor.

Im not sure is Calliope so worse than Caelus. You can use A-click for every units (eg soldiers) and both heroes. But choose Caelus give you best A-click "abusing". But every heroes missions already based on A-click and pixel-hunting later (not so bad if we get normal hero and normal fighting with something more that 1 mouse button gameplay).

And every version have some minor bugs with tech (bonuces from tech tree) (like +5% armor for every unit work only for soldiers and Hero who already have armor - but that in old now version).
Current version have MAJOR bug with HARPIES - they jump even if nowhere to jump and deal more damage that it should be.

Game too much overpriced for what it have. And now after EA status end there is no more discount > that 20% (only bonus content discount sometime for really low price).

Thats a shame. I was super looking forward to picking it up too. Meh ill hold off till i see more positive feedback, thank you for the input

Yes it is. They failed in some minor things that they can do better. Idea in general still very good and unique.

Normal campaign missions - based on survival - is good enouh to try. They more balanced than random survival. Some minor and easy to improve things exist, yes - but it a RTS after all. We dont have much of them to ignore.

In campaign you get maximum (collect everything on Hero missions) 10050 points of about 14200 required for full Tree. And it looks like almost everything you can get - but no, it enough only for technology/buildings/units and Train. No any upgrades (armor for units or more resources from any mines/farms/etc).
And you cant reset it for more later tech upgrades.

It make some fruu effects. But for first try maybe better cheat whole Research Tree.
Only Heroes and hero missions is really bad. U just A-click and use pick up grenades (sometimes) on some very large maps. Sometimes with unlimited respawned zombies - and you should also get hero to exit after complete objective.
I thick everyone understand that minor things except developers. They should add grenades as rechargable hero ability, or keep it as pivk up - but than create something for hero. In actual game hero just soldier who can only shoot - if no pick ups around.

Still it good to try. But only in Steam. You get Workshop - and it like for Warcraft 3 - best content are from custom maps/mods (for custom survival). Game itself reaaly good as engine for custom mods games, but map editor still not so powerfull like Warcraft 3.

Survival do not have techs - but use randomised Mayors. Some custom maps probably use possible upgrades not matter which Mayors game give you. Or you can do own map with own modifiers for everything.

UPD: In case if you want to try campaign, here is online calculator for Research Tree (again, only 10050 points)
http://melanite.net/tab/
Some minor missprints are there... And probably a bit of outdated (im not sure)