What attracts me to a forum initially?
Good, positive and constructive discussions and nothing of that Goat and Fedal ad nauseam stuff.
Most general forums (unfortunately) are now very players oriented (Federer and Nadal) rather than the game itself, so the less I see it the more I am interested in that forum.
A forum that offers lots of variety (all sorts of off topics) and keeps an open mind and allows anything and everything without being judgmental. This allows posters to grow.
A forum that doesn't carry the format of 'likes given' etc. Certain posters stick with other posters and stick to what they like to hear and that's an obstacle as often times they tend to promote wrong and biased discussions.
Anything that is not inherently negative or positive.