MH can be played with or without the CPP. Although the CPP is very useful as it adds not only the extra stick but extra shoulder buttons as well. Something that wouldn't be there if Nintendo had added a second stick natively. That's something both the psp and vita lack a second set of shoulder buttons. It really hurts the Vita as there are a lot of ps3 ports on it which of course make use of the extra shoulder buttons of the DS3, something vita lacks.
The second screen is very useful. Having always on mapping, reducing clutter on the main display. Whenever I switch from playing DS Castle ania games to GBA Castlevania games I always have to get used to manually accessing the map.
Auto-mapping in dungeon crawlers is also great on the second screen. Last year my girlfriend was looking into picking up Lost Heroes (a dungeon rpg) and she was trying to decide which version to get the psp one or 3ds one. She went with the 3ds version simply because of the excellent always on Auto-mapping second screen as it's very useful.
I'll take a second screen over a second stick any day. (You can have both on the 3ds with the CPP.)
starcraft: "I and every PS3 fanboy alive are waiting for Versus more than FFXIII.
Me since the games were revealed, the fanboys since E3." 
Skeeuk: "playstation 3 is the ultimate in gaming acceleration"
