Pokemon Mystery Dungeon EOTS is a good successor that improves upon the original in more ways than one.
The main plot of the game is that you're a human turned into a Pokemon, but you can't remember anything past your name. You wash up on a beach, and are found by another Pokemon who ends up becoming your partner. You become a Rescue Team apprenticing under Wigglytuff's Guild. While there, you find out about a strange ability and strange Pokemon, and about the mystical Time Gears. It's an innovative story, far from the usual as far as Pokemon plot lines go, but it's a very enjoyable and original (If you're not counting the others in the series, of course) plot line.
The missions available are varied, but always boil down to the same few basic principles: Defeat the Pokemon, get an item, rescue, or escort. But it's not such a bad thing, considering how the wide variety of Pokemon, Dungeons, and Items provides some variety. Game play boils down to randomly-generated dungeon crawling to complete these missions, using an assortment of moves, items, and abilities to fend off the unfriendly Pokemon and reach your goal. Over time, the story develops into something you can take a lot out of, through the characters and what you learn along the way.
You can also get help from Pokemon who you recruit later in the game. After defeating the Pokemon, it may ask to join your team, and will aid you in your quests. I this way, you can eventually play as any Pokemon in the game, and there are tons of them to find and recruit. You can only have 4 Pokemon on a team at a time, but you can swap these out as long as you are not in a dungeon.
The graphics are simplistic, but they have a certain charm to them. The colorful backgrounds make the terrain varied. The Pokemon are recognizable in the maps, and the overhead view works well for the game. Nothing was difficult to determine what it was, and in the context of the game, they were simplistic enough as to not detract from the dungeon itself.
Replayability in this game stretches far beyond what you might expect. The storyline extends through the after game, and even after that you'll find yourself coming back to this title. One of the main reasons for this is that everything is randomly-generated. No dungeon is ever exactly the same, even if it's the same place you just visited. The missions are enjoyable enough that you'll keep playing for a long time after the main story line has been completed.
EOTS boasts a few differences from Time/Darkness. There are now 19 choices for a Hero (21 total Partner choices, as Meowth and Munchlax are not playable as Heroes). The game also contains two new features. One is Spinda's Cafe, where you can take the Gummies you have collected to gain more skill points than you would have normally. The other is the Recycle Shop, where you can trade unnecessary items for ones of more value. At both places, you can occasionally discover new dungeons to explore. Another difference is the addition of Lookalike Items, items that have near the same name, but with little differences. As a result, they have different effects. An example would be the Oren Berry. Oran berries restore health, but Oren berries have an entirely different effect.
The main difference between the two is the addition of Special Episodes. These are unlocked at certain points in the story, and use a different, temporary save file. Any items and money you get are moved to the main game when you beat the episode, and you can give up at any time if you wish. I really enjoyed these episodes, and found them to greatly enhance the experience. Not to mention it was nice to have the back stories on some of the characters and such. They were a fun addition, and served to break up the main story a bit more.
There are a few forms of multiplayer in EOTS. The first of which is the use of DS Download play to send a demo dungeon to someone who doesn't have the game. I thought this was a great way for new players to get a feel for the game. Unfortunately, it's not quite multiplayer, as only one person plays. In fact, you could even go to say that the Mystery Dungeon series really doesn't have much multiplayer. It does, however, have Wondermail S codes. These are the codes sent if you need to be rescued in a dungeon, or used to get certain items or Pokemon. Unfortunately, they're ridiculously long and complex, and one slip up means you have to rewrite the whole thing after the mistake. It's completely unnecessary to have passwords be that long.
All in all, PMD EOTS is an enjoyable dungeon crawler set around the Pokemon universe. It's innovative to the series, and more than I expected to get out of the game. Replayability is fantastic, and it shines through its low points. Even if you've played the main game before, the story line still feels relatively fresh, especially since you probably won't remember the entire thing.