Pros
I am Legacy Markit. We used to have a "Start Up, Can Do" approach which was refreshing, but cash was always tight. Staff are usually prepared to do what it takes to get things done. The office is lovely, if a bit cramped and the overall benefits package is pretty good compared to some places.
Cons
Now we have been taken over, the sole focus has been on tightening costs. No decision is ever taken without a thought to impact on costs. Senior Management are driven by costs and savings at every turn. Middle management tend to be bully boys and yes men. Promotion to very senior levels depends on sycophancy and who you know. Since the merger there has been a totally unco-ordinated re-levelling of grades which has resulted in a lot of discontent. They have also taken the opportunity to get rid of anyone who's face doesn't fit. At lower levels staff are treated as cannon fodder and there is a high turnover. The HR Team are much better at firing than hiring. However everyone is encouraged to be a happy clappy and buy into whatever trendy eco/charity/arty project is popular that week. Most people don't, but if you want to get on, get involved and it is a way to get noticed (obviously nothing to do with your ability to do the actual job you are employed for). The highlight of any Quarter is the Town Hall Meeting where senior management come in to patronise you for an hour, tell you how well the economy drive is going, update you on recycling targets and waffle about some allegedly uplifting experiences.