Pokémon Mystery Dungeon: Explorers of Time & Darkness, like most Pokémon games, has two versions. Time and Darkness play nearly the same way as the previous games, (Red and Blue Rescue Team), but your main duty is to explore, rather than rescue.
As with Red and Blue, the main character is turned into a Pokémon, and his memory wiped clean. There are several legends lurking around, including that of the mysterious Time Gears.
Your partner Pokémon wants to form an exploration team, and explore the world. You can be one of sixteen Pokémon, but only 13 of which can be your partner.
The game features a great number of dungeons, and all 491 D/P Pokémon are in the game. (Shaymin and Arceus aren't.)
However, not all of the Pokémon are obtainable without trading to and from the other game, as is the case with all Pokémon games.
Whereas in the previous game, you used passwords to send S.O.S, A-OK, and Thank You mail, Time and Darkness use Nintendo's Wi-Fi Connection to rescue players, although Passwords and DS-to-DS are still available if you prefer them.
Another new feature is the availability of Eggs as rewards for missions. Your Eggs hatch into a baby form of a Pokémon from the dungeon you received it for exploring. The Eggs will hatch with some random Egg moves, like the traditional Pokémon games.
You can also obtain treasure chests filled with a number of rare, powerful goods.
While all elements of Red and Blue do return, such as linking moves, the game is very different from the previous games. You will not in any way, find this a repeat of Red or Blue Rescue Team.