Twitter.com currently has more than one version. There's a new unified desktop/mobile version, and more than one "older" version for "unsupported" browsers.
The legacy version is not the previous, pre-unified version (which for now, can be obtained by spoofing certain User Agent versions).
The legacy version is fairly narrow, small text, small icons, and has only a single column. In other words, it looks like a design for old mobiles. It looks really old - I think it's not really optimized for touch, although it's technically possible to use.
The "legacy" version is not good. E.g. viewing the text of quoted tweets requires a click. (Or two in my case - because it asks to reconfirm that you want the legacy version). But certain aspects of the latest version are so infuriating, that I'm not inclined to keep using it.
I'm wondering if there's a nice technically clear way to force the legacy version, and keep the progressive enhancement. Other sites let you do stuff like this. E.g. Facebook's (surprisingly functional!) legacy mobile version - you can just visit https://m.facebook.com/ But legacy twitter doesn't use a distinct set of URLs.