Ultimately I find that the companies that Nintendo typically works with these days lack a clear identity that makes them distinct from Nintendo's internal teams. Like they just make the sequels that Nintendo themselves doesn't have the time to work on. One thing I loved about Rare was that they made games that were as good as Nintendo's but had a distinct style to them that made it obvious that this wasn't some EAD game, it was a Rare game. Silicon Knights is the butt of jokes these days but Eternal Darkness was unique and different from typical Nintendo fare. I liked that a lot.
Much of the appeal of third party support is variety. You get different devs with different ideas and approaches and styles. I remember when Nintendo made a big stink about having Sega and Namco working on F-Zero and Star Fox and it just demonstrated to me how Nintendo does not get the whole damn point of third party support. Sega's F-Zero turned out to be great but if they didn't make it, some Nintendo team would have. We didn't gain anything from Sega's "support". Now if we got Virtua Fighter out of it, okay, there's a game that isn't already on the console and is very different from anything Nintendo provides themselves. Back in the 2D days third parties like Capcom, Square and Konami were a major contribution of the "Nintendo experience". They made lots of games for the NES and SNES and those games were different than Nintendo's first party offerings. The combination of all those developers resulted in a very strong library of games covering a variety of styles and genres.
I don't know what Next Level or Monster Games truly bring to the table. It seems to be that their best quality is taking directions from Nintendo. How did they leave their mark on a Punch-Out game that is so derivative that it literally has only one new character or a Pilotwings game that literally lifts level structure right out of Wii Sports Resort? I'm glad they didn't **** this stuff up but being competent isn't what I'm looking for in a developer. Needless to say I'm not looking forward to the next game from those devs because they'll just be some generic Nintendo sequel. If Next Level turned it down, Nintendo would just find some other dev to do it and the game would be exactly the same. They're pretty much just outsourcing the grunt work.
What would impress me would be a dev team with its own unique style, working on their own creation, that is different from what Nintendo themselves would normally make, and with Nintendo's role being mostly to ensure high standards of quality. I would like all games to be as good as Nintendo's (or as good as Nintendo's game WERE ten years ago) but I don't want all games to play like Nintendo's.