I installed the trackpad, but it was not behaving correctly. Took it apart again and reinstalled, using the 2 new foils that go under the trackpad keeper screws (my old ones were kind of mangled, probably from all the force I had to use on the old trackpad). I also made extra sure the trackpad was precisely lined up this time. Voila! A nice, sensitive new trackpad.

Thanks, iFixit!