Google+ and Gundotra's lasting, and perhaps perverse, legacy to Google is the "social glue" that forcibly connects together most Google services.
That Google+ never quite managed to take on Facebook is obvious. A much bigger and intangible cost, IMHO, is the falling trust in much bigger Google products like search, YouTube etc. as Google+ was shoved down user's throats.
To wit, I don't use Google+, but thanks to its bundling I've also stopped logging in to any Google service on my laptop except on a strict need-to basis (for e.g. log in, update Google Drive doc, log out...or turn GPS on, use Google Maps, turn GPS off).