reviewable.io handles that very well too

(but it's a hosted service)

Yay, thanks, looks amazing.

Being hosted is not always a bad thing, thinking in the cost of maintenance it can deserve the price.

At GitLab we also think it is a great feature to bring formally into the software development workflow https://gitlab.com/gitlab-org/gitlab-ee/issues/896

Yes, that is the first thing I look for too! reviewable.io, is the only other I know of that handles this.

Phabricator handles it well thanks to its Arcanist CLI tool.

As I understand it, Phabricator largely avoids the problem because it is primarily patch-based and not branch-based? How would arcanist handle a force-pushed branch without simply starting a new review process?

Exactly, it sidesteps the problem by decoupling branches and code review. A review request is just like a diff in a mailbox. It'd just update the diff.

It's really close to the Linux kernel development model and it scales very well.

What do you see as the major problems with gerrit?

I checked Gerrit before and like its philosophy of enforcing atomic commits and linear history, but I do not like its way of adding special change id in commit message and push to refs/for/master. That makes new users confusing and makes it difficult to follow. So I build a gerrit gatekeeper in GitPlex to enforce same rule in pull request, that is: when you need to update a pull request, you must amend your previous commit followed by a force push. No special change-id or the magic refs/for/master will be necessary.

It's simply horrible to work with. It's a mystery to me how people actually review code through that cumbersome interface. Tracking a larger patch series is just painful, and I usually had to use other tools for doing the actual work. To me, Gerrit is not a tool for doing reviews, but more like a bureaucratic behemoth from project management where you have to click the right buttons and fill out the necessary forms, so that things somehow get merged. It's more like applying for a mortgage or doing taxes.

Gerrit's current web UI is awkward, but the backend service really has the fundamentals down, and it has a first-class REST API. I used that to create Gertty which is a console UI for Gerrit that makes reading and reviewing code (in a terminal!) easy and fast.