Nintendo's peak 2D days ended with SNES, imo. And their peak 3D ended with N64. Not that they don't make great games still, they do. But I don't see the innovation that I saw during the N64 days anymore. Even Gamecube (for the most part; it had it moments, though) was a market step down.
But modern Nintendo is definitely at their best when making 3D games. Without a doubt.







