What were its drawbacks and downfalls?
I don't have a lot of experience with bullpups, but my enchantment with the compact design wilted after one exposure.
The firing mechanism is extended and subject to flex and drag. I don't think "crisp" will be in the description of bullpups trigger pulls.
Loud. Your ear is placed near the the chamber and ejection port for standard configurations.
Brass is ejected closer to your body in the standard configuration.
A bit awkward to manipulate the magazine, on those that use magazines, being that it is positioned closer to your arm pit.
Shorter sight radius. Your eye is now up by the chamber.
Perhaps more risk since you head is next to where everything goes bang.