Ello first impression (from my social media geek point of view):
I immediately spot one significant differentiator for Ello: its two channels, Friends and Noise, which allow for similar but essentially different browsing experiences, creating one more intimate, Facebook friend-like feed, and another public, Twitter follower-like feed, each of which users can absorb depending on what state of mind they're in while staying on the same platform. Dual valuable utilities = good.
These two channels also provide a means by which people can migrate those they're following between the two channels according to value. Really interested in someone on your Noise channel? Move them to Friends. Does someone on Friends post content that’s proven as less must-see? Move them to Noise. Either way you're still monitoring someone you find valuable for some kind of input.
Yes, you can do this in Facebook with lists but those are unwieldy, on Google+ in Circles - and those are great (yay for G+), and on Path in Inner Circles (but only as a narrowing filter), but nobody cares about Path.
We'll see if anyone cares about Ello as we go, but having that key differentiator may be a start.