I quite liked the first Niko movie. It had decent animation, great characters, original idea and a storyline that managed to keep me invested and then some. I've seen it once or twice since and solidified my opinion: it's more than decent Christmas movie, not a classic, but still enjoyable and kid-friendly. I'd happily recommend it to all families.
And then there's the sequel, which follows the traditional way of offering more of the same, sans the novelty. In this case Niko is once again being forced to play the rule of a headstrong child with short temper and no patience whatsoever. It's a common cliché that the main character in a sequel seems to have learned nothing from his previous adventure, and this is true here as well, which is immensely aggravating. And when the storyline pretty much mirrors the previous film, this film can pretty much kiss goodbye to being as good as the original.
Luckily the film makers got a few things right. I complain about Niko having learnt nothing, but there's the mitigating factor that he's still a kid, so he still has lots of learning to do. He should have learnt at least something, though. The rest of the cast though remains pretty much the same. They're not amazing, but they're solid. The same with animation. Nothing groundbreaking, but it looks good, though a bit uneven, as numerous studios were involved in the process, so the quality wavers a bit from time to time.
The biggest problem is the story. It's just not as good as the first one, mostly because they tried to recycle the same plot, but with different enemies, which rarely works. There's a subplot concerning Niko's new stepbrother, but it's also very tired and clichéd. Not horrible, per se, but not very good either. You can pretty much guess how it'll go from the first minute of it.
So that's this film. It's nothing spectacular, if anything it's a bit below average, but it's harmless fun and it's not going to hurt or upset your kids. It's over an hour's worth of semi-decent family entertainment. If you can, watch the first one, as it is much better, but this will do in a pinch.