With the original Wii, I feel like there were some obvious trends, some that came out right away, some that arose in time. A few of them off the top of my head:
Sports collections
Other mini-game collections
Point and click shooters (often in the horror genre)
Point and click adventure games (more on WiiWare, I guess mostly from Telltale...)
Gritty-over the top violent games (an odd trend for the Wii)
2D Platformers (mostly the 2nd half of the Wii, mostly from Nintendo, but there were some others)
It's tough to predict with the Wii U, but here are a few that I think will catch on:
Chase collections (I think this will be the new sports collection)
Other mini-game collections (yeah this trend will never end)
Zombie games (probably mostly ports, if ZombiU does well)
Other ports... in a random, mostly unpredictable fashion
Um... I dunno. What else? I guess it is still too early to see any major trends.
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