If you compared it with the previous batch, Digimon World DS, you'll notice that:

*D1: Digimon World DS
*D2: Digimon World: Dawn/Dusk

D1: the enemies are very much easy to beat, even at the later stage. (after you had degenerating a few times)
D2: the enemies are MUCH MORE STRONGER than the previous series. *Spoiler - Imagine that you're fighting the first boss which is around LV 35!

D1: you can only choose the place to visit at the portal and couldn't view the exact environment for the places.
D2: a map had been implemented and you can use the D-Pad and point to the place where you want to

D1: Quest system is optional. You can just finishing the main storyline without completing the quest system as well. It's just functioning like an extra yet useless features.
D2: Quest system had been renewed. You will need to complete a certain number of species quest(s) before the Union Quest can be available. Note that the Union Quest is exactly the main storyline where the story proceeds.

D1: Less digimon.
D2: More digimon.

D1: When viewing the Digimon stats, it didn't states the weak and strong attributes for the digimon. (Need confirmation)
D2: Weak and strong attributes for each digimon had been added. Note that the weak and strong attributes differs for each digimon, independant on their species type.

D1: The bosses are MOSTLY easy to defeat, with condition that you had degenerate and digivolve your digimon a number of times, >5
D2: The bosses are quite STRONG, but you should be able to defeat them followed by the aforementioned conditions.

D1: It doesn't take much time at all to meet a variety of digimon
D2: It take longer time to meet a certain digimon within a certain place.

D1: You gain your tamer rank by gaining Tamer Point, which can be accumulated by completing the quests.
D2: You gain your tamer rank by entering and WINNING at the battle arena. You need to win only 1 battle and the battle is REALLY HARSH! You'll know what I meant once you aim for Gold Rank.

Just my personal thoughts.

After completing DW: Dusk, including the Platinum rank. I decide to play DW. Dawn now. Quite boring.