Pros
Some truly brilliant people, catering, competitive pay, fun stuff you actually get to play with, and some very fun travel with everything paid for.
Kontras
...if you can stay on the right side of office politics, the above is all you have to worry about. As others have mentioned, the politics is toxic and managers and HR are too stretched to notice. The soft, start-up tech culture is enjoyable but paper thin. Constant finger pointing at every level is how people cover their back and is rewarded. I've worked in some intense places but never seen so much shifty and expertly executed passive aggression as a norm. If you're willing to turn a blind eye to constantly seeing people getting sneakily shot out the airlock because their face doesn't fit, or overworked, or bullied, there are some serious careers. The money is washing out the gamer culture rapidly.