Command is a very mediocre game because what it did right was counter-balanced by what it did wrong. I wrote this whole rant about it over on the forum Maxi lured me over to, i'll try to dig it up if i can but it's probably not even worth it.
Assault wasn't a terrible game, with some Nintendo polish it would of been better but still not a great title like SF64 was. It's sad because the potential to expand the series was all there, just executed piss poorly.
SF Adventure shouldn't even be brought up in the argument because it wasn't a Star Fox game. No i'm not saying that to troll the fanboys (cuz i'm one of 'em!) or because it deviated too much from the SF formula, i'm saying it because its TRUE. It was N64's Dinasaur Planet revamped for Gamecube with Team Star Fox shoe horned into it. Basically, thanks to Nintendo themselves the Star Fox series nosedived (pun intended!) after the second installment. Way to go.
All they need to do is make a Star Fox 64 2.0 with an in-house dev-team to bring the series back to a respectable place, so whats the fucking hold up? Once Star Fox is known as a good series again, they can tweak the formula to include things introduced in Assault and Command just fix them so they don't suck ass. Like no more furry fan-fiction!
edit: Caterkiller brings up one of the reasons SF:C was crappy; it was strictly all-range mode "levels". A new Star Fox game should have a mix of both types of levels, but the all-range levels can't be so fucking bare bone like they were in SF:C (and SF64).