I liked Factor 5 a lot. RS 3 wasn't as good as the rest, but I still enjoyed playing it. Especially since you could play Rogue Leader in co-op. I think the fact that they're making something different will be good for them. It'll give 'em the chance to try new things (well, besides on-foot missions- guh). But, I won't play Lair for a really long time.
Even though I do feel like Rare isn't as good anymore, it'd still be good to have them aboard. I've heard Viva Pinata is good (which suprised me).