Though it doesn't seem to have been announced yet I noticed the Tribes of the Vale rules have been posted to the support page.
Each clan seems flavorable and powerful in it's own right. Sorta like getting three mini-factions rather than one. The new crag terrain seems fun and like it will create some interesting battlefields though I wonder if we really needed more lakes. The expansion seems token heavy but I'm fine with that for this expansion as their very unique abilities is what makes the Clansmen feel different than standard house troops. I do hope it doesn't become the new standard however.
This expansion follows Lords of the River in including more flavor art which I also like as not a lot of text is in these books anyway. I wouldn't mind if they started putting in a little map of the Riverlands showing where the battles take place though. I think that would be neat. I've actually printed out a nice map of the Riverlands and been marking where I estimate the battles take place as I play through them myself. It doesn't make it a campaign but it FEELS sorta like one as the scenarios do chronologically follow the novels.