Grunn is essentially one big puzzle, there's many endings, most of them are technically just different "game overs" and one of them is the good ending, in theory you should be finding more and more pieces in each run to eventually put them all together and get to the good ending however there were a few too many bumps in the road that kept this from being a smooth enjoyable experience for me.
First of all since you're going to be starting the game over and over again it gets pretty disorienting to not have any sort of inventory to check and make sure which items you have and have not collected on the current run.
The Polaroid pictures (hint system) are good enough to nudge in the right direction sometimes but some other times it's very unclear what it is they want out of you.
There's also a couple of confusing elements like a certain key item appearing in different places each run and also somewhat unclear progression flags, there were a couple of passageways and the like that did not properly communicate to me how it was that I activated them.
But that is comparatively small potatoes, getting to my bigger issues now, the game has too many red herrings you can chase after that just end up wasting your time if you're trying to beat the game, like getting all the instruments to the kids or following the whole magpie quest.
This is my biggest issue with the game, since the main quest itself ended up being really underwhelming and was in dire need of more pieces to make it up, pieces that were in the game but unfortunately were not used where they were required the most and the most frustrating part of the experience was precisely realizing that out of the 100 puzzle pieces that I was "painstakingly" keeping track of i only needed about 25 of them (at most) to make the whole picture.