I'm sad that sync did not make it this iteration, but hopeful that it will next time. I love using Thunderbird again. I long switched off of dedicated e-mail clients and forgot what I was missing. I have had to retrain myself to not open a new tab when I'm expecting an email. Not to mention, browsing mailing list threads is impossibly better: it has a nice threaded view that you just can't get in any web interface I'm aware of. But proper sync would be nice to have, seriously. I would really like if it could sync account credentials, personally, since I have a decent number of machines and a handful of e-mail accounts, but even if it didn't it would still be useful to have some form of sync for preferences.

I'm sure some people don't like the redesign. Personally, I think it's alright: it is a bit more on the "modern" side in some regards, but it's still reasonably pleasing to use, and still not too white-space heavy, and that's all I really care about.