@alcinnz The entire user experience is a travesty.
Number one, and in my opinion, the single most important detractor: No side-by-side comparison of patches. Hate to say this, but the line-oriented diffs are not ideal for making before-and-after comparisons of the code. In my experiments with SourceHut, it does not adequately address this concern.
No (topical) in-line feedback is possible without completely marring the content and legibility of the email. One could argue this is a good thing, as it strongly rewards making lots of microscopically-sized patches that are easier to review. However, I counter that with, in my day-to-day, I find tiny patches are a once- or twice-in-a-year phenomenon. My work typically results in large-scale changes that cuts across multiple layers in the technology stack, leading to large, wide-sweeping patches that must be applied all at once for things to work (e.g., drivers, kernel, language bindings, and the app proper). Use of email for patches just isn't useful for my current line of work.
Interfacing with e-mail clients assumes you run a mail client locally, and do not make use of web-mail or "integrated" mail clients like MS Outlook. Unfortunately, at work, we use Outlook and webmail interfaces depending upon need. My personal mail needs is also covered by webmail. Importing and exporting messages for use with Git is possible, but it is an additional burden which, bluntly, is remarkably error-prone if you don't pay attention to what you're doing.
I'm not going to say that it's superior or inferior to alternative methods; but for my current work-flows, e-mail patch management is just not a good fit. I'm sure it's great for those who have good supporting tooling surrounding their workflows, and for those who have teams who buy in to having tons of really, really tiny patches instead of a few rather larger patches.
At the end of the day, it all depends on the preferences of your team mates and the needs of the project.