But 'meh boring' is not the same as well-regarded.

Isn't the point of a good UI to not get in the way? If that's the case, then whether or not it's been well-regarded might be best determined by the "meh, boring" factor, regardless of how much users/critics/etc are aware of that fact.

In other words, an absence of 'oh god help me' ought to be well-regarded if it isn't already. :)