It's nowhere near as bad as critics were claiming, but fans of the series will be sorely disappointed with this one.
However, if you can look past the weak dialog, flaky acting (Nicola Peltz is fucking TERRIBLE), slight storyline changes, lack of comic relief, and cringe-worthy alternate character name pronunciations, you'll still find a good chuck of entertainment here (I'll never grow tired of the fighting/bending scenes!).
Even with that said: If Nickelodeon was smart, they would hire a new director & screenwriter for the next two movies (Books 2 & 3). As for M. Night, he should probably put effort into killing himself. Let's just hope he doesn't fail at that too.