TL;DR: SoL is one of the best Sandbox games out there if you are willing to put the time into it, and I can not recommend it more if you are into that genre.
Signs of Life is a breath of fresh air (for me, at least) in the survival-sandbox genre. Most games in said genre tend to visually resemble eachother, or play identically (i.e. make a crafting table, then furnace, etc...).
SoL manages to differentiate itself from the lot, mostly thanks to it's (although minor) storyline and lore.
Sure, it has pickaxes, mining, 2D voxel worlds and the likes, but it offers much more than the run-of-the-mill sandbox game.
Having played for a good couple of hours now, I've made it to the point where I've acquired the Level 2 Access Card, and have explored the 4 structures that I've found (I'm certain there are more that I've yet to discover), and am starting to get a nice collection of gadgets, and technologically advanced items.
However, at multiple points during my current playthrough, I started getting afraid that I might have gone through all of the content, due to the fact that I had no new recipes that seemed interesting, nor could find anything of interest that I had access to either. Though, I will admit that when I 'did' discover new recipes and the likes, I couldn't help but pull a massive smile, knowing that my playthrough wouldn't be done anytime soon.
In it's current state, the game has huge amounts of content (most of which I haven't even discovered yet), and quite a bit of potential. I'm hoping that the content shown on the trailer will be soon added -if not already-, as I'd love to find larger bases, ruins, and more content to explore.
SoL is by far one of my favourite games in the sandbox genre, and could easily compete with, or even surpass games like Edge of Space, Starbound or Terraria, if enough work is put into it in the coming months of it's development.