Quick review 9/20/07 edit #1
Islands start out blank and can hold 4 digimon and can have 2 gadgets and give you 0 XP in each species type and have 100% growth rate(how much the species XP gets multiplied). In Dawn/Dusk you get to buy a terrain board for your island which will control what it looks like and BGM Music. Terrain boards are very important. They not only seriously increase what type of Species XP your island produces but also allow you to expand on your islands memory which controls how many gadgets and digimon you can place.
You better choose wisely though because installing terrain boards is permanent. BGM boards or back ground music boards I havent touched. They increase the growth rate of some species XP but DECREASE another species xp by the same amount. That is great if you want an island specifically for helping digimon get a certain kind of XP but not so great for an all purpose island. Terrain boards didnt have any negative effects.
Digivolving got a slight tweak(probably to get rid of the stat roll back bug found in Dw.DS). In the previous game to evolve to the next form you would have to reach a certain level like 12. Then after you evolved you were lv12 or even higher. The XP it takes to go from lv12 to 13 is alot more than it takes to go from 1 to 2 which made it hard to improve your digimon as you climbed the ranks. Well now when you evolve or devolve you start out at level 1. So even if you evolve into a higher form its still easy to level up. There are still all kinds of requirements in place to level up though like stat and species XP, and friendship levels. But those arent really a problem.
You can still make your digimon powerful by evolving and devolving but because stuff always start out at level 1 your stats improvements wont be as readily visable as before. Its not until you actually level up and evolve back up to a higher form that you will see the difference but you do improve.
They also brought in DNA digivolving that lets you squish two digimon together to get new digimon or digimon that are changed in some way. I havent messed it yet so i dont really know what you can do with it. You can also armor digivolve.
Oh unlike DS where you got missions from the digimon on your farm you now goto a place in town to accept them. After you do a couple of quests for individual digimon then you usually get a mission from your tamer team. Doing quests gets you tamer points, a fat wad of cash and equipment and items. In the beginning you should definately try to do them first so you have the cash to make some great improvements to your island.
If you have a DS you have to own these games man. They are just awesome. MUCH more satisfying than digimon. You can make your digimon into gods if you work on them enough.