The main disappointing one was probably vBulletin 5 as it felt incredibly underwhelming compared to what it could have been.
I’ve got to agree against vBulletin’s price point, I don’t know how the paid software get away with charging absurd prices but, I suppose that there’s always someone who will pick it up regardless of the price.
Only problem with infinite scroll is that it doesn’t always remember where I left it on the page which creates a slight issue but, it’s not the end of the world.
As for signatures, really depends on whether some admin wants it or not which is really just more customisability for forums although, people tend to use it overwhelmingly for advertising which isn’t that great as opposed to other potential uses.
Immune to Xrumer spam? I wasn’t aware of that feature.
XenForo pretended to be a bit of a revolutionary although, I never did get the benefits of it as it just looked like yet another competitor to me as opposed to Discourse where you look at it and it instantly stands out from the rest of the competition.
With revolutionaries which fail to deliver entering the market quite a bit, it’s good that someone is taking a new stance to it all as opposed to the more traditional approaches.