Eh, I love the game but even I can't bullshit myself that hard, they absolutely did promise more than it currently is.
https://www.kickstarter.com/projects/crateentertainment/grim-dawn/description said:
Grim Dawn won’t hold your hand to ensure you never make a bad decision and it won’t feature a story on rails with linear level design to prevent you from ever getting lost. It will, however, offer you the chance to do things in your own way, have an experience that is unique from everyone else playing the game and explore off the beaten path to see and do things that not every player is likely to find.
[...]
There is no one central story; there are many stories and whether you help the weak or help yourself and how you go about it is yours to decide.
[...]
Feature a more open-world design with randomized elements that will greatly enhance replay-ability. Each play-through will be unique with "set-piece" spawners that can turn a patch of wilderness into different types of enemy camps, a traveling merchant caravan, etc, each with their own unique art.
We don’t control where you go; you do! If you don't want to follow the main story, you aren't forced to. Non-linear progression allows you to unlock new areas by repairing bridges, defeating enemy blockades, etc, as soon as you have the resources and power to do it. Race ahead into higher-level areas and get pwned, we'll warn you but we're not going to stop you!
There absolutely is a central story and it's completely on rails and linear. As for having open world design... Sure, you can enter Act 2 areas when you get the resources to do so, but you wont progress past Homestead or Fort Ikon if you haven't progressed enough in the main quest. And between Devil's Crossing, Homestead and Fort Ikon it's just a linear corridor.
Every playthrough is basicly the same. There are no "set piece spawners" that mutate areas to be unique, just different blocked passages.