The CG animated genre is one of the toughest out there because quite frankly the standard is so high that anything less than a stellar effort will draw criticism. Amongst live action movies maybe one in ten are considered good or excellent whilst the rest are mediocre or crap, in this genre though around one in ten are considered duds whilst the rest are excellent. "Shark Tale" defies categorisation as its quite simply the most middle of the road CG movie I think you'll ever see.
Oh sure there's some inventiveness such as an oceanic Times Square and little tributes to modern culture first utilised in the "Shrek" movies, but the overall film is just bland despite a big name cast. A lot of the blame can go on a simply uninteresting story which tries to be essentially a 'street cred' urban tale of a guy wanting to be a 'playa', gets there by defrauding the public and finally has a minor crisis of conscience and comes clean. Throw in an astonishing amount of product placement and potential merchandising and you have an ft almost insulting beast that seems more assembled by marketing gurus than actual filmmakers.
"Shrek" or the assorted Pixar movies worked because they made the great comedy seem easy - the gags came thick and fast and fit into the mould of the story. The "Shrek" movies and "Nemo" in particular worked well because they combined adult humour, self-referential parody and a genuine heart to them. "Shark" has no heart whatsoever and the humour tries way too hard, opting for more visual spoof sight gags and attempts at humour by the unfunny cast (eg. Oscar's movie line quoting at the end) as opposed to the casual almost flippant but far smarter wit in the likes of "Nemo".
Despite its big name cast from Smith to Jolie, the ONLY person who does a decent job is Director Martin Scorsese who's occasionally amusing as Oscar's attitude-switching boss. The Italian mafia stereotype criticised in this is far less offensive than some of the other characters such as the rastafarian jellyfish or the almost racist overtones of Oscar himself who acts like a rap star wannabe (not helped by Smith who WAY overplays it). Whereas "Nemo" was cute and inventive", "Shark Tale" is bloated and icky. Toss this piece of old sushi back in.