I guess I care the most about their older IP. Mario (3D more than 2D unless with new art that is not New art), Zelda, Metroid (pre-Other M), F-Zero, Kid Icarus, Punch Out!, Wave Race, Donkey Kong (Country), Star Fox (though Zero mostly ruined that series for me), Fire Emblem (on console, though that series might be over-exposed currently in some ways...). I hope Nintendo will surprise me with a few Switch sequels or reboots for those. Metroid, F-Zero and Kid Icarus would be at the top of my list there.
That said, some of the older popular IP I have far less affinity with, like Pokemon, Smash and Kirby, all of which I never truly got into and mostly ignore nowadays. Mario Kart I used to love greatly but the later installments did less for me with their greater online multiplayer focus and resulting widening of tracks and the increase in kart part unlocking and such. I'll continue to keep tabs on new MK games though, just in case.
As for relative newer IP, Luigi's Mansion, Splatoon and Pikmin are some that I like quite a bit though they all run the risk for me of getting stale at some point due to how similar each sequel is in terms of art and atmosphere (compared to some older IP that get changed up far more on those fronts between games, Zelda and 3D Mario for example). I will continue to support them for a while still though. Wii Sports (Resort) is another more modern one that I like and I really hope they will revisit this series on Switch with its joy-cons in some way as it offers an experience that is still very unique. Animal Crossing is one I really loved on the Gamecube but never managed to get into again due to the change to the rolling world design and Nintendo's handheld focus. I would give it another chance on console though.
Hopefully the Switch will end up with a healthy mix of rebooted/revisited old IP (in the vein of Kid Icarus: Uprising, Metroid Prime, etc.), sequels to active IP that offer familiar yet new experiences (like Mario Odyssey and Breath of the Wild), new IP (similar to Splatoon, Mario Maker or ARMS), and collaboration projects with other Japanese devs / publishers (like a new Mega Man with Capcom, Castlevania with Konami, or a Metroid with FROM). That would make me really happy.
Edit: I'd also love a new Battle Clash now that I think about it, even if it is an obscure series nowadays. A shame how the Wii never got a reboot of that. More puzzle games in the vein of Dr. Mario, Wario's Woods and especially Tetris Attack would also be appreciated (or even ports of those).
Edit 2: I feel that Wario (Land) is also ripe for a comeback or reboot perhaps. I love the Wario Ware games and would like to see sequels to those, but I'd also love to see Wario star in something else as well.