It's solid animation occasionally on par with one of these 3D animation movies (which is obviously the goal). However the storytelling is quite chaotic, incoherent-feeling and hyperactive. In particular, I find the dialogue and character interaction lacking in this regard. One couldn't really expect it to stand out as clever and "well-written" anyway, and it also doesn't exceed expectations by being about as shallow as can be, however in addition to that I find it unnecessarily annoying.
It is kind of a given that there is somewhat chaotic interaction between the undercover aliens and the humans, which serves for a lot of the "humour", however the dialogue and interaction between the aliens themselves (mostly brother and sister) is equally messy and erratic, with constant talking past each other and pointless side-remarks, which seems like a try-hard attempt to have constant conflict and be interesting, but which just results in the watching being kind of strenuous and not really pleasant. (I also find the boy in particular lacking in any sympathetic traits and even his voice odd and too old-sounding.)
I still deem it essential "holiday entertainment" right now, and a fairly fun blend of science fiction adventure and everyday slapstick, but it obviously could have been better.
Review of 3Below: Tales of Arcadia
