I got a free Lumia 640 from work, and switched from my old SGS3 with work SIM to the 640. Sure, the apps are a bit lacking, but I've never used apps too often anyway. For me it's Facebook, email, browsing, and it's just fine for that. I much prefer the live tiles over IOS or Android, it's by far the best mobile desktop IMO.
The real benefit for me it, after months of using it, it's just so fast and fluid, even on a basic phone. Even after a full reset, TWO of my SGS3 just slowed to being unusable, and that's with virtually nothing installed. The 640 even beats my daughters HTC One M8 for speed. Android has really disappointed me over that last year.
As others have said, maps are really good and the in-built sat-nav rivals TomTom apart from speed camera alerts (which cost). Free with the ability to download, very impressive.
Cortana is useful too, I never used Google's version, but use Cortana all the time.