The biggest strikes against it for my groups are:
1) it's not D&D (or even d20 based), requiring all new system mastery.
2) it's perceived as another system where you're a weakling and have to run away from everything.
3) the implementation on Roll20 is lacking (no character builder, no official adventure content)
I get where they’re coming from. I suspect if I wasn’t a fan of earlier editions the first point would put me off.
The second is entirely dependent on how challenging the DM makes it. I don’t think WFRP is a game where PCs are weak... in fact quite the opposite. Fortune and Resilience means they can be very successful. However it is a game where sometimes things go wrong... very wrong. I’ve played a fair bit and I don’t think my party has
ever ran a way.
I feel the third, particularly at the start. Luckily the game isn’t really one where levelling your character is a big process. It’s far more granular than that. It isn’t like D&D or where you have a small number of major decisions to make, you have a large number of very minor decisions. A lot of which are random. IMHO the best way to create a character in WFRP is to randomize it as suggested in the book. Amending things if you feel they don’t fit.