Comparatively weak single-threaded performance, weak GPU performance, constrained memory interface, high power consumption when not running only the companion core.
Tegra 3 isn't terrible, but just like previous Tegra chips it was so hyped up before launch and again turned out to be among the weaker ARM chips of its generation. Exynos, Snapdragon S4, Apple A5 (and now A6) and OMAP 4 beat Tegra 3 on everything except synthetic multi-threaded benchmarks (because it has 4 cores, obviously).
I don't know about the GPU, my impression was that it was competitive (the single-channel memory interface probably doesn't help), but otherwise that's spot on. It really seemed to be a design whose main goal was to have the most cores for marketing purposes.
And of course they launched on a process that was just about to become obsolete, and haven't been able to do a shrink. Not sure why, though. Complications with the companion core? Just NVidia's general inability to get 28nm to work?
(Commercially it didn't help that they were unable to get access to a competitive LTE modem. That meant there was no shot at the US phone market. But that's not particularly a failing of NVidia, everyone but Qualcomm has that problem.)
Tegra 3 isn't terrible, but just like previous Tegra chips it was so hyped up before launch and again turned out to be among the weaker ARM chips of its generation. Exynos, Snapdragon S4, Apple A5 (and now A6) and OMAP 4 beat Tegra 3 on everything except synthetic multi-threaded benchmarks (because it has 4 cores, obviously).