The film is a bit of a curate's egg but on balance I'd say the good far outweighs the bad.
The storyline is interesting and the film is beautifully photographed and pleasant to look at. The direction is good too.
As for acting amongst the leads, well Ben Stiller, Jack Black and Danny McBride all play themselves as they always do, so you know what to expect there. They do a competent job of course, as they should do. Matthew McConaughey turns in a respectable and interesting performance as Stiller's agent. But it's Robert Downey Jr and Tom Cruise that take it to a different level. Without either of them the film would be a lot less pleasurable to watch.
They bring a depth to their characters that the script probably doesn't deserve. Cruise in particular was quite mesmerising when he was on screen - makes you realise what a fine actor he can be and what may yet be in store now he's older and may be offered more character driven parts.
I don't think the film is going to make anyone's list of must see movies but it's worth at least one viewing, if maybe not a repeat one. But that said, having seen it once now if I saw it was on TV I'd happily watch it again