Ask a devoted gamer to make a short list of the best games of all time and there's a good chance that Ico will make an appearance. Indeed, due to its relative obscurity, Ico is often enthusiastically promoted to more casual gamers by its rabid fans, and offered up to non-gamers as a paragon of the medium.
This is actually kind of a shame. Just as an understanding of the history of cinema is needed to fully appreciate a movie like Citizen Kane, a deep personal history with video games can raise the experience of playing Ico from merely enjoyable to revelatory. This game generates rabid fans for a reason.