Pros
If you get a thrill from working on a recognizable product that's often in the news, then being at Twitter will provide you with a psychological boost. Strong engineers. Twitter is a frequent OSS contributor. So even though Twitter has a lot of in-house tools and runs its own data centers, you will still get the chance to work with tools that are probably used elsewhere. Good food and plentiful coffee. The company tries hard to be inclusive.
Cons
Location: mid-market is not the most convenient part of the city. I get the sense there is a lot of tech debt in the product, but a lot of effort has been made in the past year to pay it down to make future development easier. A lot of turnover in the revenue team's upper management ranks. Exec turnover is quite high, even though exec compensation is frequently in the news for being way too generous relative to the company's revenue level and growth rate.