Snappy has higher memory requirements, takes up more disk space. Flatpak is implemented in about half as much code (granted with slightly different feature sets) despite being written in C rather than Go.
And despite these signals, I don't see any broad community "antagonism" towards Snappy at the moment. You can find an angry blog post on almost any topic, doesn't mean the opinions are popular. I don't feel any particular way about it since it seems to do something at least a little different than the competition. For example, Flatpak only really tries to sandbox desktop applications, much like .app directories on OS X.
It is a little suspect that Canonical always shows up with their own version of something which everyone else (SUSE, Arch, Red Hat, [Oracle/Novell]) mysteriously can't even manage to build and package successfully. In the case of Snappy, I think it's more or less a coincidence that it started within seven days of Flatpak. It might turn out to be better (or serve a completely different purpose). Another thing in favour of Snappy is that at least snapd and snap-confine (but not snapcraft!) are widely packaged for distributions other than Ubuntu.
The thing is, the rest of the industry is running on independent contributors. These independents manage to widely distribute and standardize on the best. Meanwhile, Canonical consistently goes off on their own and builds something that ultimately nobody can even package (Mir, AppArmor, Unity), let alone adopt.
Canonical clearly wants to differentiate, and that's entirely their right, but their differentiation factors often seem to wither and die after a couple years of bragging and some small progress.
