I just finished playing the highly praised game Braid. I really enjoyed playing it, even though at some points I was very tempted to use a guide, as some of the puzzles got me too puzzled. But putting the game down for a few hours (or even some sleep), definitely helped as one easily loses creativity when playing it long. It is very interesting how the brain seems to continue to work on the puzzles, or to get used to the game mechanics, as it seemed to me much easier after a break.
Other than that I was very amazed by the atmosphere it creates, especially the music and the way the story is presented. Very simple, but one always wants to know more. The story itself is quite vague and sometimes even confusing, but fit very well to the overall game.
Should you like solving puzzles á la Portal and not have played it, then there is no way around this gem!