Pros
The people at G Research are all very smart and good at their job, from the quants and devs to the IT support. You don't meet any weak links. The support/infrastructure is very impressive. Everything you need to enable you to do the job you need to do, the interesting bit, is in place. I came from academic research at a top institution. There has been no step down in intellect in the people around me, quite the opposite. The support and infrastructure are beyond what can be imagined in academia. The people are friendly and approachable. People go for lunch together, not really eating at the desk. There's a lunchtime running club and well attended company drinks, as well as informal outings. There is little of the highly strung internally competitive atmosphere typically associated with finance. It has an almost academic feel, but people are more productive! Everyone is ready to help you with anything needed. There is no hours culture. Just a culture of being productive, thorough and intelligent. Perhaps a 40 hour week is normal for a quant. Great place to work.
Cons
While there is plenty of sharing of methodology and general understanding, critical information about the particular approach you are taking are not shared by default with anyone but your manager (and their manager etc). Before arriving, I was naturally concerned this would hinder my learning and damage the collaborative atmosphere. It doesn't. And if you want to work for G Research long term, as I do, then you will fully appreciate the fact that this means no single person can walk out the door with all the best ideas, which would severely damage you personally. In the current system, your contributions tend to be long lasting as they stay secret, which is good for you. If you want to work at G Research for 2 years and then move on, taking all the best ideas, then it's not so good and you're not the type of person the company is looking for.