I watched this live for the first hour or so. Looks like you can only get cosmetic value out of the paid battlepass, all power milestones are advanced simultaneously for those who have the free or the paid progression. While I wish it wasn't like that for a game you're already paying box price, I don't really mind, cosmetics are just cosmetics, and if it allows the game to keep the highest quality standards in exchange for skins or mounts that have no impact in the gameplay, so be it.
Some of the features they talked about sounded quite good, especially related to dungeons, bosses, or endgame challenges, but will have to see them play.
Other than that, the seasons look enticing but it will be 6 weeks before season 1 starts alongside the first battlepass. On one hand, I feel that's a bit too long of "dead time", but then it should give people more than enough time to finish the game and get their account-wide unlocks without feeling forced to spend too much time on the game.