Having just watched it, I can confirm that 'I Am Mother' is definitely well worth your time, and more than a cut above a lot of Netflix's usual output. It's certainly a slow burner, and has a VERY minimal cast list, but very well acted nonetheless. Lead Clara Rugaard really delivers, reminding me of a young Natalie Portman. She gets plenty of meaty stuff here, and there's some great character development as the screenplay twists and turns.
The set design is pretty impressive, and there's some very neat visuals, particularly in the second half. The synth heavy score works well with the tone, and I'd recommend cranking up that home cinema kit, as the sound design is very good - all clunking airlock doors and pipes hissing. It keeps the attention when dialogue is at a minimum.
Sure it borrows a lot from a million and one other sci-fi movies (Moon, Ex-Machina, Oblivion, Alien and the confined setting of 10 Cloverfield Lane spring to mind), but if you're a fan of the genre, it's still got plenty to say, and an interesting message.
I won't comment further on the film for fear of spoiling things, but as usual (and particularly in this case), you should avoid the teaser if you haven't already seen it, and just dig into the film.
I going to give this 7.5/10. I wouldn't watch it again anytime soon, but then that's just down to it being a slow burner, and having already unearthed it secrets.