Agreed, that's why I wrote free interaction, meaning the same kind of freedom you have in the other dimensions. Achron is the only concept I know of that has fairly free interaction with time. However, there are a number of games that have deeper interaction with time than just save games, consider the variety of games that now offer some sort of "rewind" feature of the kind pioneered (afaik) by Prince of Persia: Sands of Time.