Bootstrapping the local infrastructure.
Think of it like a game. You start off with a lathe and a CNC mill and some 3D printers and a bunch of other stuff. You now need to grow crops on Mars. You need to refine Iron ore and produce high quality steel. You need to manufacture plastics, glass, concrete. You need to mine water ice to make water. You need to use electrolysis to make Hydrogen to feed the Sabatier reactor that makes Oxygen/Methane from the atmosphere. You need to explore, you need to maintain and expand the habitat, you need to facilitate future flights to make them as easy as possible and to build capacity for offloading passengers and equipment smoothly and quickly. And then you need to figure out how to use locally produced steel, aluminum, concrete, glass, plastics, etc. to build more machine tools, to build more habitats, to build more farms, more life support equipment, etc. How would you build a backup generator system that ran on LOX/Methane using local machine tools and locally produced materials, for example? How would you build high pressure gas containers for life support systems in habitats using the same?
All of this is like The Martian times a million. It'll be go-go-go every day, because the amount of work remaining will basically be infinite for your entire life. Once you "solve" one "problem", once you advance the state of Martian industry, agriculture, technology, etc. by one step, you're really just opening up the problem space further. The kind of people who will do best in this environment and those who are extremely capable, self-reliant, inventive, goal oriented people (basically workaholics).
They could have plenty of freedom, but if you're not 100% dedicated to working to build and advance the colony you probably won't get along with the rest of the colonists. If you don't obviously bring something valuable to the table (which doesn't need to be industrial/technological/agricultural elbow grease, and could easily be things like being a musician, artist, reporter, chef, even a poet, etc.) you'll probably have a bad time. But on the plus side, if you are a very results-oriented, goal oriented person, you'll likely have a lot of freedom. You'll be able to build, experiment, "hack", and explore to your heart's content. For the most part you'll be able to have your pick of interesting problems from day to day, you'll be immersed in a sea of experts in various technologies, all of them eager for apprentices to come learn and help. And at the end of the day (well, years anyway) you'll be able to look back and say "I built that, and that, and that, and that" for values of "that" equal to significant parts of the local industry and ecosystem. Imagine being part of the team of people who built the first structures to house the first Martian forests. Imagine having your name stamped in the side of the first iron foundry or steel mill on Mars. Imagine having your hand prints in the concrete of the first habitat built using local materials on Mars. That's what being a colonist will be like. It'll be some of the toughest work, but also the most rewarding.