Well, I'm not too much of a movie-goer, and my brain tends to shut down whenever I go into a movie (probably a defense mechanism of some sort), but I do not take kindly to the following cliches:
Evil CEO, Repentant Hero: This doesn't exactly ruin the movie, but it does put an indelible stain on its greatness. I'm sick and damn tired of having the bad guy be an evil corporate executive (because there are no decent CEO's, right?) and having the good guy realize that they're evil and join the other guys (Na'vi, prawn, human resistance, etc.). I aspire to be a wealthy businessman myself some day, and I know that just BEING one doesn't make you evil (Tony Stark and Lucius Foxx, anyone?). Granted, corporations can do some distasteful and unscrupulous things in the name of profit, but that's because they're trying to make the most money for their investors, and not maximizing profit for your investors is actually illegal (in America, at least). Also, I'm tired of the protagonists being little whiny douchebags who can't just do their job without having some sort of moral dilemna. I like protagonists to stick to their guns.
The Source of the Modern Age: This one DOES ruin the movie for me. Whenever a certain plot device is heralded as "the source of the modern age," i.e., it was reverse engineered to create all of our modern technology (like Megatron in the 1st Transformers movie, which I saw, unfortunately), the rest of the movie might as well not count, because I become so overcome with rage and disgust. It is despicably disrespectful to our scientists and engineers who worked their whole lives to invent the technologies we rely on. To suggest that it all just fell from the sky is essentially invalidating their lives' work, and it pisses me off.
One more thing: I happened to walk out of Splice, but that was because I thought it was gross and I was about to throw up. The rest of the movie was alright, but I can't bear to look when you combine sexuality with something as hideous and unnerving as that Dren creature. Blech...