The Lumia 650 is a downgrade from the 640

I don't think anyone would really want to upgrade it from L640 but it can be a great alternative... I've been using L730 and had to get L650. Let me tell you that I'm not really disappointed. The performance is somewhat similar to L730 (so it has to be similar to L640 too). In fact win10mo is much better on this phone.. So you can't argue that SD212 is a real downgrade... FFC too is 5mp versus 1mp of 640...
 
I don't think it's a downgrade as it has a slightly faster processor and a better FFC camera. Also, it's design is awesome, far more beautiful than L640 but not as beautiful as my L830 IMHO.
 
It's a tale of give and take....

Microsoft gives you a better screen, premium build quality, improved cameras, Windows 10 on board...then they take away $200 of your hard earned money on a underwhelming processor / RAM combination that gets the basics right and arguably not much else. Still, the 5" size is a sweet spot.
 
I upgraded on Cricket from the 640 to the 650 and love the 650. Thinner, better looking, better screen angle viewing. Windows 10 works just fine on it. Syncs easily with my laptop. My only complaint is I don't like that Windows 10 is getting away from the pivots menu style, and using more hamburgler menu's. For example, for my simple use, I liked the native Windows 8 music player better than the Groove Windows 10. But the 650 for me is just about perfect. I just can't see spending the kind of money for any of the premium phones on any platform.
 
If you are already on Cricket, $129 for the Lumia 650 is not a bad price. But for unlocked / $200 it can be considered debatable.