I bought a Moto E at the same time as a Moto X for my wife as part of switching from Verizon to AT&T. I've had it activated for a week now, and so far I'm really impressed and was expecting less for the price. So I'll share the following early impressions, negatives first:
For a kid or teen, the lack of a front camera, and a poor-to-fair rear camera with no flash, may be disappointing. Very minor for me though...
The 4GB memory almost put me off from buying the E, but so far its ability to put compatible apps on the sd card is working out. I cannot imagine using the E without an sd card. So far though I don't have lots of apps on the phone, and time will tell if 4GB is enough. EDIT: I think I'm mistaken about apps going to the external sd card; I believe only certain media actually moves there if an app allows it.
Only other negative for some might be the small size, but I do a lot on my Nexus 7 when I want a larger screen so I like a compact phone. My wife's X os as big as I'd want.
Otherwise, all good. The phone is pretty quick, runs 4.4.2 without hiccups, and gets good reception and clear sounding calls. The screen is decent, not brilliant in bright light but good overall.
Overall, for reasons I can't totally put my finger on, it just seems really solid and not cheap. I got it as a temporary phone, thinking I'd give it to one of my kids when the successor to the X comes out, but I think I could live with it a long time.
Hope that's helpful...