It's frequently considered by critics to be one of the greatest video games of all time and is one of the best-selling games on the Wii with over seven million copies sold worldwide. Upon release, Super Mario Galaxy 2 was met with universal acclaim, and was considered an improvement over its already-lauded predecessor, with its creativity and technological improvements over the original receiving high praise, although its high difficulty and story (in comparison to its predecessor) received some criticism. Among the additions are dynamic environments, new power-ups, and the ability to ride Yoshi. It was later decided that the game was going to be developed as a fleshed-out sequel when the development staff continued to build upon the game with dozens of new ideas, and so development time expanded to two and a half years. The game was originally planned as an updated version of Super Mario Galaxy this version would have been called Super Mario Galaxy More. Mario must travel across various galaxies to recover the Power Stars in order to travel to the center of the universe and rescue Princess Peach. The story follows Mario as he pursues the Koopa King, Bowser, into outer space, where he has imprisoned Princess Peach and taken control of the universe using Power Stars and Grand Stars. It was first announced at E3 2009 and is the sequel to 2007's Super Mario Galaxy. Super Mario Galaxy 2 is a 2010 platform video game developed and published by Nintendo for the Wii.