Speaking at the San Sebastian film festival in northern Spain, where he presented his film "Snowden," Stone said many in the US had grown disillusioned with a president they once saw as "a man of great integrity."
"On the contrary, Obama has doubled down on the (George W.) Bush administration policies," said Stone, whose latest movie is a biographical political thriller about Edward Snowden, the former intelligence contractor who revealed a vast US surveillance programme in 2013.
Obama "has created... the most massive global security surveillance state that's ever been seen, way beyond East Germany's Stasi, way beyond that."
"In the name of one thing - terrorism - to change all the rules is not a marginal response, it's an extreme response," he told reporters.
"Let's beware of fascists and tyrants who tell us 'we are going to protect you'. I don't want that."
This is far from the first time that Stone has dabbled in politics, having directed "Platoon" about the Vietnam War, "JFK" and "Nixon" among a host of other films.
He insisted "there was no agenda" behind the release of his latest movie just weeks ahead of US elections, but said he hoped Obama would pardon Snowden, who currently lives in Russia after escaping his homeland.
Actor Joseph Gordon-Levitt, who plays Snowden and met with him to prepare for the role, said the former contractor "was embarrassed" that a film had been made about him.
"He's a private person, he felt awkward about it," he said.
The San Sebastian film festival, which takes place in the northern Basque country until Saturday, is the highest-profile film event in the Spanish-speaking world.