It may have been a collegial place to work at one time. The focus on moving up the rankings has killed that.
The firm touts its rankings as a great place to work. First, several of those rankings require an initial payment to be considered. Second, the firm treats its administrative staff very well, and the staff boost the rankings; associates' experience is quite different from staff's. And third, the firm has no tolerance for any sort of "life interference;" I spoke to associates who took time off for illness, parental leave, or disability and had their bonuses reduced.
Associates are expendable cogs in the profit-generating wheel. So long as associates bill, the firm does not care if they are mistreated, disconnected, or they burn out. Associates constantly try to one-up each other, so there is much stealing of credit and throwing under the bus.
The firm will take any opportunity to cheat associates out of their bonus, to the extent of punishing those juniors who get a bad review from impossible-to-please managers. I got stuck working for a manager who literally refused to work with anyone else. Even though no one else was good enough to work with that manager, I was still penalized with a substantial bonus reduction when the manager bashed me in reviews (then turned around and added me to a new matter).
Partners have no interest in training associates, and no patience when associates do not instantly and magically know everything. Because Cooley markets itself as a cost-effective firm, matters are often staffed too leanly for there to be a senior- or mid-level associate to whom the junior can turn for guidance. I had matters that were staffed only by a partner and me, yet the partner still refused to answer strategy questions. (I was not stupid enough to ask a partner questions about substantive law I could research myself; I asked about the direction I should take for the client.) This was in my first year, when I had never handled any similar task. I only had 1-2 questions per week...and the partner still refused to answer them.
In short, it's like any other BigLaw firm. The difference is that Cooley won't admit it.