IMO, they should put 10 worlds in the game, plus a special Bonus World.*
You know what they say...
The more, the merrier. And quite frankly, more fun.
Each world with their different and respective themes. Like in BK/BT.
*Now, as for the Bonus World, in a case where they implement a similar system to the Stop N' Swop, (in a post here, I said that they should include items: nine similar items, plus a final item) they should make this world last greatly. I was thinking that once they gather all the items, and the door or "poster-portal" opens, the passage way should be something similar to the Victory Road from the Pokemon series, all the way to the final stage/level.
What do you guys think?
"INSERT TO F***ING BOX!"