About six months ago I went to see
Dan In Real Life, an altogether unsatisfying film that should have been much better than it was.
( minor plot spoilers )The problem with it was the tone was entirely uneven. Two thirds of the film was exceptionally well written and acted, touching, simple and very human, with shades of grey everywhere. The other third was funny, cute and rom-com, where everything was tied up neatly. The problem being that these two things clashed _terribly_.
When I see an action movie I either want a tense thriller that grips me with its realism, or a daft over-the-top explosion-filled nonsensity - straddling both areas at once is incredibly hard, because I can't believe in a character as real _and_ as a cartoon.
Which isn't to say that cartoons can't be emotionally effective - I cried at the end of WALL-E - but I need a world that's tonally consistent, selling me a world that's gritty and real, and then throwing in a cartoon moment will tend to destroy my emotional attachment unless it's done very well.
All of which is largely to agree with the article here on
The Aliens of London, which goes to great lengths to explain _why_ it doesn't just fail to work, but it acts to destroy everything around it.