Hard to advise as tastes differ so much and you've covered a broad range of genres. The gentle calm of Animal Crossing must be the total opposite of the button mashing frenzy in World Ends With You!
I recently got World Ends With You, assuming it would be a more 'grown up' game than most stuff that comes out for DS. (yeah, I'm Ye Ancient Olde Gamer...). I was totally wrong - the presentation seems completely aimed at the teenage market, perhaps even the younger end of that. The game is strong on hip-Japanese culture, trendy-teen fashion, J-Pop soundtrack and the kewl dood teen speak is more-or-less unintelligble to me
(
I admit to having neither any knowledge or any interest in any of these things. However....after a shaky first couple of hours (the game is confusing at start - perhaps deliberately), I'm now really enjoying it!! Fighting on 2 screens at once seems a crazy concept, but is uniquely satisfying when you finally *get* it. And I'm even enjoying the J-Pop
So I can recommend this game if you're prepared to try something very different. Looking at your age, you'd probably understand what the kids are saying, too!
Pokemon is Pokemon, I'm sure you know what you're getting there.
My son regularly plays "Canvas Curse", I think it's supposed to be one of the best Kirby games. Apparently like the GBA Kirby but makes good use of the NDS styles & screems.
Animal Crossing is virtually a must-have for DS. But very, very slow going. My children and I all have had our own Animal Crossing towns for over a year now. (how sad is that?) As single player, it's a bit too dull, you really need WiFi and others to connect to to bring out the best in it.
Don't know about Digimon. Isn't it supposed to be a more 'grown up' Pokemon style?
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Circular logic is correct because it is.