The 3DS will do well.
I remember when the DS was first unveiled, all the haters called it a quick cash in and a sloppy knee-jerk reaction to Sony's imminent foray into Nintendo's domain. All the 3rd parties supported the PSP, initially, but once the Big N decided it was time to unleash some quality, intuitive games that served to showcase the system's strength, 3rd parties hopped aboard and the DS made the history books. It's only a matter of time before Nintendo will - once again - lead the charge and release a series of megatitles for their newest system, which will lure the timid 3rd parties back to its camp.
Nintendo is actually a smart developer. They know the right type of games to create at the right time and for the right audience. They're not as stupid or one-dimensional as Sony who can seemingly only cater to the urban jock-gamers while making a few pitiful attempts at luring other markets (e.g., Resistance, Loco Rocco, etc.) only to end with embarrassing results.
I will say, however, that Nintendo seems to be dismissing the formula that helped them to achieve their success, which is creating an inexpensive gaming option for the mass market and making evolutionary changes to said option from its predecessor. But, nevertheless, if their 3DS games are great and original AND FUN, which I'm sure they will be, nothing will stop its success.
