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Except for the smallest of PRs, we many teams eschew GitHub reviews in favor of a third-party app called Reviewable (demo video). Reviewable has an incredibly dense UI: you could probably master a new musical instrument faster than you could master Reviewable.
Still, Reviewable is far better some teams have decided that Reviewable offers a better UI than GitHub for large changes that undergo multiple rounds of feedback. The basic model is the same: a diff of your change where your reviewers can leave inline notes. In Reviewable, unlike GitHub, every comment spawns a new thread of discussion, and the UI will highlight any threads that you haven't acknowledged/responded to.
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You won't need to do anything special to enable Reviewable for your PR; one of our bots will be along shortly after the PR is opened to post a link to the review interface.
Check with someone on your team if to see what your team prefers, but even if your team does not use reviewable for sending each other reviews in your day to day work, you will still want to be familiar with it if for reviews on changes that cross team boundaries.
Addressing feedback
If someone leaves line comments on your PR without leaving a top-level "looks good to me" (LGTM), it means they feel you should address their line comments before merging. That is, without an LGTM, all comments are roughly in the discussing disposition, even if the Reviewable disposition marker in the bottom right corner hasn't been set as such. If you agree with their feedback, you should make the requested change; if you disagree, you must leave a comment with your counterargument and wait to hear back.
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