Pros
You get Harvard on your resume
The Expos program is a great bubble within Harvard of kind and thoughtful leaders
Good (immediate) colleagues
Cons
When I first took this job and was so excited to work for Harvard, someone offhand said "oh, you have a job for the Crimson Cancer?" I laughed, thinking that they were joking.
They're not. Harvard is a rapacious marketing firm with a vague educational branch. The faculty positions are catty and cutthroat, and taking a preceptor role means being treated like someone with a GED not a PHD by the university. By second semester, even the first years know that you're gum on Harvard's shoe and tend to deprioritize your course. There's no job security -- in fact, a guaranteed firing at 8 years -- and salary is significantly lower than the same job at peer institutions. They ride EVERYTHING on the fact that you will get to say you worked at Harvard, but that doesn't carry the sway you think it does.
Caring about students and their outcomes kept me motivated, as did the direct little friendly world of expos. And for a first job out of grad school it is better paid with better benefits than most. But it is also a CV killer if you want to teach anything other than writing - if you're in any discipline other than English, buyer beware.
At the end of the day no matter how much you love your students and colleagues, and no matter how good your direct management is, working for an institution that disdains you will get you down.