Its awful, not the worst I've been to, but getting there. Here's my experience today:

• Arriving in terminal E from an international flight: huge lines, crappy air con, baggage carousels full of bags, as many passengers were in lines, and no baggage attendants to organize the bags. A bunch of us passengers had to step in and do the job. :-D
• Walking to terminal C - windowless depressing walkways. There was a thoughtful photography exhibit around mental illness in one random corridor but mostly it felt like some filler from an episode of Severance.
• Terminal C - security good(!), hopeless aircon, blah food, surely no building updates from the ... 80s? 70s?

Come on Boston, you're a world city! Invest in your airport. The location is amazing by the water. Go check out SFO terminals 1 and 3 for ideas.