Star Fox 3D is simply a glorified expensive port of a N64 game you could buy for $10 on Wii Virtual Console. So I would rent it at best. Don't get me wrong it is a very fun game, but your mileage will vary. Once you learn the stages and have gone down all the paths there isn't much else there to see.
Mario in this case is a built from the ground up 3DS game. It has a ton of levels and manages to keep that Mario charm. If you own a 3DS I would consider buying it, but it doesn't feel system seller to me.