Pros
Addgene understands and embraces the buzz-words you'll often hear companies toss around to attract candidates: "team focused", "employee centered", "work life balance". They are open and receptive to feedback to make things even more magical. The overwhelming vibe in the office is positive, supportive and inclusive. There are no 'cliques' and everyone is welcoming. There is an excellent balance of fun and dedication, with many fun (and sometimes goofy) events in the office. The events are not the awkward ones you often find where you feel forced to participate. There is thoughtfulness involved with planning these events to ensure there is really something for everyone. Introverted book nerd? There's a book-club for that. Social butterfly? There's a beer hour for that. Want to just get to know your fellow co-workers on other teams better? There are goofy competitions such as a rock-paper-scissor competition. Overall, there is the general feeling that everyone trusts and respects everyone else's work 100%. The caveat for this is that if you're just looking for a plain old job, 9 - 5, where you can do the minimum and not look beyond the code lines in front of you... this is not the place. I think the workplace here is so great because everyone has fantastic work ethics and takes pride in the quality of the work they produce, which I understand isn't for everyone. You can't have your cake (all the awesome magic-ness) and eat it too (just getting by).
Cons
The only "con" I have is that Addgene IS a non-profit. I do believe the salary for software engineers to be competitive for a non-profit. Which is, unfortunately, not as competitive as industry. *HOWEVER* there is a phenomenal benefits package that definitely offsets this.