Oh, you’ve asked a question where it’s impossible for me to be brief. Sorry.
I’ve worked at both agencies and in-house (several times for both). They are a bit different, but the random differences between any of those individual jobs has been larger than the differences that I could attribute to it being because I was at an agency or because I was working in-house.
I suppose an agency job has a wider variety of work, but even that’s not necessarily true since people there tend to get pigeon-holed into working with certain clients. Anyway, depending on the in-house job, there might be all kinds of variety depending on the size of the company, the nature of the products and services, and the size of the creative and/or marketing team.
There are other differences that are mostly just procedural kinds of things, like time-tracking and billing issues usually being more rigid at agencies as opposed to in-house. And yes, agency work can be stressful, difficult, demanding, unstable and cutthroat, but it can also be exhilarating, fast-paced and exciting at times. Then again, all of this depends on the agency, its size, its longevity, its specialty, its background, its location, its financial stability, its clients, its culture and its owners.
To me the biggest consistent differences between agency and in-house situations arise in the company culture and upper managements of both.
The senior management at agencies are in the business of advertising and marketing, and have succeeded largely because of their savvy and business acumen in those areas. As a result, the culture at most agencies is generally conducive to and supportive of good work and talent since those at the top have typically spent their careers in the business. That’s not to say that other problems don’t exist, but the people at the top generally understand the business. The big, mega-agencies are a different story of sorts, but that’s another tangent.
In-house creative and marketing teams, however, are typically odd fits within their companies whose top management structures and company cultures are built around things that have little or nothing to do with advertising, marketing, design, writing or whatever.
For example, let’s say the company builds widgets and has an in-house team to help market those widgets. This widget-building company is focused around engineering. The people at the top, for the most part, all came from engineering backgrounds. They don’t really understand marketing very well, and they believe in engineers and exude an engineering mindset. They know they need to market their products, but they under-appreciate the skills and processes required to do so effectively. They tend to view their marketing/creative team as a not-quite-trusted support or service group that exists to implement those things the brains in the company — the engineers — want done.
There might be very talented people on their creative/marketing team, but at some point going up the chain of command, someone with an engineering/business background is calling the shots and making the hiring decisions of who will lead this in-house team. Consequently, out of ignorance, the wrong people are hired, and this incompetence filters down into the creative team as illogical work assignments, counterproductive processes, widespread frustration and poorer results.
The extent and specifics of this dysfunction differs from one in-house situation to the next, but I’ve never been in an in-house group where some variation of this bias that relegates the creative/marketing team to a lesser role doesn’t exist. And typically this problem is worsened by the group ultimately being overseen by someone that upper management trusts but who has little background, experience or aptitude in any creative or marketing fields.
As for employment ads for companies looking to hire those with outside agency experience to lead their in-house teams, well, again, I think this goes back to what I’ve mentioned. The higher-ups in these companies who do the hiring know little to nothing about the business and they lack the background to select the right candidate based on demonstrated abilities. So they end up relying on superficial shortcuts, like insisting they come from ad agency backgrounds. More often than not, they’ll end up hiring a big talker who couldn’t cut it at his or her previous agency job, but who managed to fool those doing the hiring.