I'm sure Heaven has changed a good deal in 25 years. Jeremy moved the regular Thursday / Friday / Saturday G-A-Y events there after the city forced the Astoria to be closed and torn down to build Crossrail. Now that was a really fun club! Some found it a tad dirty and seedy, though I think that was part of the charm and character of the place.

Unfortunately Heaven isn't big enough to regularly support the big name acts like those who used to headline when the club was at the Astoria. However, they still get British pop stars to show up at Heaven from time to time on Saturday nights.

Back to the OP -- hopefully you know that World Pride is in London in July, with the main parade over July 7th. I've been there for "normal" London pride a couple times and had an amazing time -- quite an impressive parade, big events in Trafalgar Square, and Old Compton Street and Soho Square packed with partiers. One year I saw Sir Ian McKellen speak at the rally in Trafalgar Square, and the next year Lady Gaga was live on-stage at Heaven (though I never got in the club that night because the queue was down the street).

It can be a fantastic experience, but all the bars and clubs are going to be packed to overflowing that weekend. I think it's well worth going if you don't mind crowds and you go in expecting that sort of experience.