"Flappy Bird" received "mixed or average reviews" from critics, holding a Metacritic score of 52/100, based on seven reviews. The app was criticized by the "Huffington Post", which described it as an "insanely irritating, difficult and frustrating game which combines a super-steep difficulty curve with bad, boring graphics and jerky movement". IGN gave the game a mediocre score of 5.4 out of 10, quipping that the game is as addictive as it was shallow. Despite criticizing its playability and its "no skill" requirement, IGN noted that the gameplay made it "an addictive short-term distraction" for the casual skill and score-obsessed players. The game's difficulty has been a source of ire for many users, with one user stating that it took him half an hour to achieve a score of five points. According to its creator, the game is slightly easier on Android devices than on iOS. Nolan Bushnell, the creator of the video game "Pong", compared "Flappy Bird" to his own game by claiming that "simple games are more satisfying". John Romero, a co-creator of the classic first-person shooter "Doom", commented that "Flappy Bird" is "a reaction against prevailing design the way grunge was a reaction to metal." When questioned at the time by Chocolate Lab Apps, a website for app developers, Nguyen claimed to have used no promotional methods in the marketing of "Flappy Bird". He credited the sudden rise in the game's popularity in early 2014 to possibly "luck". However, online marketer Carter Thomas suspected that the developer had used bots to cause its success. When questioned on this by "The Daily Telegraph", Nguyen said that he respected other people's opinions and did not wish to comment, adding, "I'd like to make my games in peace." When "Newsweek" inquired about the matter, Nguyen wrote, "If I did fake it, should Apple let it live for months?" The game was criticised by Kotaku for what it claimed was open use of "Mario"-style graphics, referring to it as "ripped-off art". It later published a correction, clarifying that the game's green pipe was "a new albeit unoriginal drawing". According to some Vietnamese newspapers, including "Thanh Niên" and BBC Vietnamese, "Flappy Bird" is very similar to a game released in 2011 (two years before "Flappy Bird") called "Piou Piou vs. Cactus", from the gameplay (by tapping on the screen) to the main character design (a small yellow bird with big red beak) to the obstacles (green cacti and pipes).