Like most hedge funds, the org chart is very flat. You will be rewarded through comp, but if you desire more than money, the upward mobility is pretty limited.
For many years, there was a saying that Citadel is a "technology firm that happens to trade". This is ridiculous. The technology at Citadel is very outdated and many teams spend an equal amount of time working around the limitations of the infrastructure as they do building solutions to problems for the business they serve. Of course the darling businesses are allowed to buy whatever they need to get the job done, but for the other slow-but-steady money makers, technology can be extremely frustrating. This frustration transcends both the software (compilers, tool kits, etc.) and the hardware (storage subsystems, network infrastructure, etc.).
Unless you have deferred comp (difficult to achieve) or are directly involved in a business (QR and trading), your comp is based on the overall performance of the firm and yourself,. but you have no direct way to participate in the gains (or losses) of the firm. A voluntary employee fund (or something along those lines) would be nice for those of us that are dedicated to the firm and want greater benefit from our contributions.\
The office is sterile. There is very little access to natural light (unless you happen to have an office), otherwise it's a fluorescent hell. The "open cubicle" concept is extremely detrimental to productivity, but I'm not sure it was done in the name of conformance and collaboration. In reality, it does nothing to foster collaboration outside of what a team is going to do naturally, with the added strikes of being noisy and disruptive.
The politics in upper IT management can be paralyzing. We often do nothing out of fear or a Congressional-like inability to compromise, rather than stepping on some toes and doing what's needed to get the job done.