Pros:
Biggest pro is that it is the only course in Boston! It won't be a pro level course, but having a place to play in the city is amazing.
As of March 2020, there are now 18 holes. A handful are really short, but again, being able to play 18 in Boston is amazing. When and if the course becomes official with the parks department, I imagine there could be some changes.
The course overall is tightly wooded and requires some technical and even kind of funky shots. I personally think this is great because it forces you to use every shot in your bag and learn the shots you don't have yet. Since hole numbers are changing as the layout evolves, I won't name any numbers, but there are at least 4 holes that could be called the "signature" hole for the course. They are technical and really enjoyable.
Another positive is that playing on weekdays I almost always have the course to myself or run into another regular.
The park is gorgeous and the course snakes around Scarborough Pond. It's a great escape from the city.
Cons:
Navigation is probably the main issue. I play here weekly, but if you are coming for the first time keep an eye out for yellow flags to guide you. Regulars are happy to show you the way.
The number of short/ace run holes. There are two of these back to back which were added to round out 18 holes, but hoping we can see a couple longer holes to replace them eventually.
Natural teepads aren't great, but again, when and if this becomes an officially recognized course we will likely set up a club and get funding for teepads.
Other Thoughts:
The park has a reputation for being sketchy, but in the 2 years I've been playing here and working on cleaning up the course we have seen significant improvement. There were homeless camps that have been cleared out and the added foot traffic thanks to our dedicated regulars seems to have kept them away.
The course is not official with the parks department, but a recent survey sent by the city included disc golf as an option for "what do you do when you come to Franklin Park," which is a great sign. Momentum is on our side and people constantly ask me about disc golf when they see me playing.
Keep coming out and supporting disc golf in Boston!