I've bought a lot of "IoT" devices (going back to the days of X10) and yeah lot of them are utterly useless, but so were a lot of dotcom startups in 1999.

The thing I've realized, which may be obvious, is that first and foremost the device needs to work well in its "unconnected" form. Examples:

* Hue/LIFX/etc suck because most of the time I just want to flip a light switch, not pull out my iPhone to control it. I'm a fan of Z-Wave (or whatever) switch replacements that function just fine as regular switches, or I can turn off every light in my house through a wall controller, Alexa, or my iPhone. But if that secondary system fails I can still control my lights.

* Withings scales are great, because it works well as a simple scale, but also records my weight so I can go back and look at trends, etc.

* I like Dropcams because they're super easy, though I wish it weren't locked to a proprietary service