Great that ASUS is helping handheld PC gaming advance but from a consumer perspective, I cannot in good conscience recommend anyone buying ASUS products.
Their customer service is legendary for being abysmal and for something like the Ally you need good support.
It’s server-based so you need to be online to play. However you can pretty much play it solo without interacting with other players (which is how I generally play it, save the occasional events and challenges).
They’ve added significant amount of content post-launch which includes new locations, NPCs, missions etc so it’s not too bad, although I would say NPCs aren’t as well put together as other Fallout games.