***SPOILERS AHEAD***
I feel like one of the main magics of the first movie was that you weren't quite sure whether or not the whole thing was in Tim's head, or if it really happened (in my personal opinion, it was all in Tim's head). And you didn't need to know; you were able to go through the adventure through the viewpoint of a child learning to wrestle between losing "all his love" to his "younger brother," and coming to terms with being okay with it, choosing to lose it all so that he could have a brother again.
The second one basically says, "YES IT ALL REALLY HAPPENED AND THERE'S MORE!" and removed all mystery, taking little scenes here and there from the first movie and jamming it into a hodge podge of action scenes, lame baby jokes and a weird villain with a weirder evil plan. To make it worse, all the scenes with little Tim and Tabitha made me cringe, because I was having flashbacks of "17 Again" where a father magically transforms into his younger teen self and, in trying to encourage his teenager daughter to greatness, she ends up falling for him. In the scenes where little Tim is with Tabitha in her bedroom as he plays the guitar for her, when he had penned fake tattoos on himself in order to be a bad boy and was being disruptive in class, I kept cringing at the thought of, "Is Tabitha going to fall for her dad? Even this is just too much for a kid's movie." Thankfully it never went there, but it shouldn't have even made viewers (or maybe just me) think that it could have.
I watched it with my 3 year old who just enjoyed the loud noises and bright colors, and occasional references to the first movie (which she loves and has almost completely memorized). For me, as the movie wore on, I just wanted it to tie up loose ends and finish. I guess they added a tiny part at the end (where the mom answers the baby's phone and accepts a mission) in order to create a third one? I hope not.
One last thing: where's Tobey Maguire?? He was already an adult with two children at the end of the last movie. Why would they have someone completely different?