Everything I am about to say is based on me watching my friend playing on new Rare games and what I ahve heard from other people and review scores.
I don't think Rare suddenly suck, but I do think that Rare have lost their "spark" so to speak. I'm not sure if this is because a lot of the team left, or that the brothers aren't interested because they have lots of money or if it's simply the change from Nintendo consoles to Microsoft consoles.
The last Rare game I played was Starfox and that didn't have that Rare "magic" but still had the Rare feel. So I think that game was just simply an average Rare game, just like Kameo looked like to me.