I've done it twice (2016/2017) and I really enjoyed it. It was very well organized, the course is pretty flat, the bike course consists of a few loops and you are very likely to be going against the wind for half of the course but then enjoying the tailwind on your way back. It's nice to see the Boston skyline and the best part: I can ride my bike to the start line. :)

i've been doing it since they started offering the olympic.
the swim is an ocean swim in old harbor. conditions are quite variable, its been pretty calm one year, choppy the next, and canceled the 3rd. you swim into the sun for the first stretch so make sure you have dark/tinted goggles.
long T1 from the beach to the transition area consisting of sand/sidewalks/grass
the bike is flat and very fast despite the 2 no passing zones and 3 u turns per loop (4 loops for the complete course). it will start to get crowded, more so for the later swim waves. i've always gone in the open/elite wave, so by the time i get off the bike its not too bad for, for me anyway. there are 4 lanes (2 per side) that are completely closed to traffic for the duration of the race so plenty of room for passing. the road surface is ok, there are a decent amount of frost heaves, but overall not too terrible. ive experienced much worse conditions here in new england.
short t2 nothing special to note here
the run is also very flat. it is mostly road/sidewalks, ~95% pavement. i think there are 1-2 water stations per loop of the course, so that is available if you need it.
overall, it's a solid race. every year i am torn whether i want to do it again or not (based on the expensive entry fee), but always cave and do it because of how competitive the start list is and its only 20 mins away.

bike course really weirded me out. As mentioned above, pancake flat, but with 14 places, where you have to drop speed significantly. I've never seen any course like this. I guess if you like to practice your u-turns, it could be nice. I don't.

It's fine if you're local, but I wouldn't travel for it. Bike course is constant turns and slow downs. Swim was canceled this year. Run is pretty boring sidewalk route through a local ball field area. Missed opportunity relative to what you might think a Boston tri would include - i.e., Charles River Swim, run through Newbury, etc. But I understand the constraints.