This movie's point is often misunderstood, which is why that is the first thing I'll cover. Many say that its message of nonviolence is hypocritical considering that's the whole series' point, but this is not the case.
In the series, trainers battle each other for fun, as a sort of sport or recreation. Think of it like football or boxing. It's harmless fun for them, especially since their pokémon are power-brimming creatures always eager to express their abilities.
However, the sort of fighting this movie shows as wrong is not the same. Mewtwo forces his superclones to battle their regular versions tooth and nail, suppressing their special abilities. The helmet and pads are gone from the football game; the boxing gloves come off. They're no longer fighting for fun, they're fighting just to prove superiority.
If anything, this movie tries to explain this difference to the naysayers saying Pokémon promotes violence. It stresses the difference between friendly competition and pointless fighting. Again referring to sports, it's the difference between boxing and street-fighting.
Now, on some other points, I do not think this movie is unbearable for adults. The plot is pretty cheesy, granted, but one shouldn't always take things too seriously. Keep in mind that half the dialog is spoken with the character's tongue jammed into their cheek; Team Rocket especially feels the need to deliver humorously ridiculous puns such as "I wonder if [the clones] feel... Clonesome" at every turn.
As for noticeable product placement, well... it's a movie based on a show that's based on a video game. All of the characters can be seen in said video game; that's promotion enough if you ask me. There's also mountains of merchandise out there too, but as a recommendation I say stick to the games: they're actually worth the cost and are the reason I still love this series after 12 years.