The script was naff, Hemsworth was playing a comedy sidekick rather than a believable character.
All that stuff with his 'old flame' was tiresome and the action was largely lame.
It felt like this movie couldn't make up its mind whether it was a kid's comedy or teenage action flick. It didn't fall in to the comedy/action crossover because the comedy was too childish (I feel 40 years too old to enjoy the comedy) and the action (specifically the two alien antagonists) was occasionally a tad too menacing for the younger audience that the comedy was aimed at. The two alien antagonists were well done and reminded me a bit of the ghost twins in the second Matrix film.
Anyway, this was a father's day 'treat' that fell a bit flat.