Its performance is so horrible that even on a high spec machine with fast internet, you have plenty of time to click the "switch to plain ol html" button. Which is actually more in line with the performance I'd expect from a glorified file drawer.
You either have graphics hardware support disabled or youre laptop CPU is not running in perfoance mode and has its govenor set to something like balanced or power saving mode.
I don't have this issue with other sites, it's just Gmail being Gmail.