I suppose all gay men must have a reaction to BITB one way or another. It must be respected for being incredibly daring when it came out: the first play to focus exclusively on gay characters and show us as average men with basically normal lives. (As late as the 60s few plays, & far fewer films, even acknowledged gays existed; those that did used gays as symbols of abasement or decadence. 'Different from the Others'-1919 and 'Victim'-1961 were isolated exceptions.) The sexually frank dialog was also a groundbreaker. A gay friend who saw the original stage production remembers being astonished by Harold's line, 'Your lips are turning blue. You look like you've been rimming a snowman!' Crowley wins laurels for being the first playwright to present our community without apology.
That said, I admit I found the film dated when I first saw it in the 80s, when I was in my 20s. Watching it now, I have a different reaction. For one thing, I adore the brilliant dialog. What an inspiration to write a comedy of manners set in the archly mannered world of New York gays! There hasn't been a screenplay with this many epigrams per inch since 'All About Eve.'
The first act is funny and marvelous. The second act teeters into melodrama, stealing the device of all-night boozing and humiliating party games to 'strip characters bare' from 'Who's Afraid of Virginia Woolf?' Michael, the host and game emcee, is such a bitch that we can't feel sympathy when Harold confronts and effectively destroys him. Kenneth Nelson's performance as Michael doesn't help: it's like an acting class exercise, all shrieking and hysterics.
While the ensemble as a whole is strong, Leonard Frey's brilliant, definitive Harold enables him to walk off with the film. The straight Cliff Gorman does fine work as the flaming, ultimately touching Emory; Keith Prentice is very good as the one well-adjusted party goer, the happy sensualist Larry; and Reuben Greene and Frederick Combs make the best of underwritten characters (Combs get lots of chances to show his rear end to great advantage, including a gratuitous nude shot).
Besides good acting, the film has other points to recommend it. The film's 'opening up' of the play is never intrusive or contrived. Friedkin's camera never seems trapped, though almost the entire picture is shot in one apartment, and he keeps the story moving swiftly along. And Crowley shows courage in leaving the question of Alan's sexuality somewhat ambiguous, despite his affirming his wife as the person he truly loves, thereby rejecting Michael as a gay man and precipitating his collapse.
The themes of love, truth, self-loathing, friendship and relationships speak to audiences gay & straight. They are dealt with in a well made film and a script crafted with wit and humor. While the 'if we could just not hate ourselves so much' viewpoint does date the movie, it has more skill and substance than 75% of the films on the market-and (I agree with other posters) 99% of the 'gay' films out there now.