Pros
If you love Twitter and what it stands for, it's a motivating place to work. Twitter is simultaneously making solid improvements to its core product while investing in some invigorating new areas like live video, AR/VR, and AI/computer vision. I've noticed an increasing number of new hires from places like Google, Facebook, Uber, and others lately which indicates that interest is strong. Food is awesome at lunch time (not quite so much at dinner, but it's solid). HQ is a nice place to work. At least on my team, management is very good at recognizing good work and promoting quickly.
Cons
There are visible departures of well liked people, most of whom seem to be leaving for smaller startups. I feel that this is a natural part of one's career, but it can still be disappointing when people who are admired and who care about Twitter still choose to leave. Work on some teams can be slow due to a paranoia about experimenting to make sure metrics aren't hurt. I feel that leadership needs to be bolder in shipping to prevent churning and inefficiency.