Why was it good?
OR
Why was it shit?
(Take your pick.)
I want to know why I should see / avoid it.
Mostly it was corny (without the required ironic tone that would have made it acceptably campy...instead it took itself seriously and you're never quite sure why, as the subject matter is juvenile), it focused on all of the wrong things, like the three boring main characters and their uninteresting/corny relationship at the expense of the plot, there were some serious plot holes, and the acting was either bad (in the case of the kids) or large-ham-like over the top (in the case of the more veteran actors...only Travolta was okay in his hamness, but then he ended up only being in the film for five seconds.)
Basically, it spent a lot of time beefing up the main characters (especially that little boy who looks like a shaved bird) by explicitly telling us why they were awesome through the narration of the girl (he double majored in biology and business at Berkeley so that he could simultaneously grow and sell the best weed in the world without resorting to violent street tactics AND do humanitarian work around the world AND spout a bunch of Dalai Lama bullshit AND he had this random retinue of amazing bankers and scientists and computer experts as friends who could help him at the drop of a hat...you get the picture), and then diminished the whole bit about the evil Mexican drug cartel to the point that it seemed like the whole thing involved one evil lady and a gang of five Mexicans running around California trying to kill them, with the occasional vaguely threatening teleconference thrown in here and there to remind us that there was supposed to be a larger plot. Oh, and the beefier male lead was an Iraq veteran who had "wargasms" instead of "orgasms," and also had his own retinue of Iraq buddies who were not only available and willing to risk their lives for their buddy's drug tomfoolery, but also were able to casually get ahold of military weaponry like rocket launchers, explosives, and other automatic guns just because they had served in the military at one time.
I will say that it had its high points, though, and not all of them were related to laughing at John Travolta. No, in fact, there's this one scene where Blake Lively's character is being hand-fed pieces of steak by Del Toro's character for no apparent reason...just to make him seem creepy? I don't know. Either way, it was amusing in a way I don't think Oliver Stone intended. Just imagine a bunch of other absurdities like that sprinkled throughout a half-cocked story that really and truly seems like an adolescent male stoner's wet dream and you will have basically gotten the gist of Savages.