Pros
I've worked in a couple of other places before joining. AlphaSights is by far the most goal-oriented and meritocratic environment I've been in. Depending on what level you join at, within a 3-5 year timeframe you can expect to pretty much run your own show (team, clients, etc.). This is pretty compelling compared to most places I know of. The company is full of smart, driven people which makes for a stimulating, environment. While the pressure to perform is high, it is clear what drives success and how to contribute to it. This minimises politics and allows the right people to get on with things. Lots of opportunities for innovation and growth - there's an endless list of things to be done. But you have to be willing to grab them (and not just talk about it).
Cons
Company (and people) often feel stretched. Many (too many?) initiatives being pursued in parallel, leading to shortage of people. Talent bench needs deepening at mid-level and above. Too many are inexperienced college leavers who have little reference points for what working life is about. Also, in its quest for growth, the firm's hired some people with the wrong expectations - if you want a more sheltered, non-frontline 1st job, this is not the right place.