I love my (original) 3DS not just for the games but for the 3D effect quality, the sound quality, the portability, the control reliability (hundreds and hundreds of hours of use, plays just like new, and the slide pad is the best portable analog control of any portable gaming device), and yes even the OS, it's not as powerful as an iOS/android/windows device obviously but I like Nintendo's Wii U and 3DS OS way more than the Sony and Microsoft's OSes. Nintendo's customizable icon grid keeps the focus on the apps and games, and all the shopping and social features are actually fun to play around with instead of feeling like corporate mandates. Tons of nice little touches like the rabbit who tries to sell on you on the new streetpass games or the unwrapping presents and how much they want you to doodle things on the touchscreen. Nintendo's OSes have very nice virtual keyboards as well, I prefer them over iOS honestly.

Battery life is annoying though, and the unpleasant glossy plastic surface on the original 3DS at least I will also agree with.