Ubisoft + $1 for a month

is AC:Valhalla any good?
Longer than it needs to be but the combat is solid. Pretty much abandons the "stealth assassin" game in favor of Viking berserker but it's a damn fun time doing it.
is AC:Valhalla any good?

Middle of the road. Was buggy, better now. It is a very long game, about 100 hours if you don't most of the main quests. The story is a bit odd in that you don't have to finish all story/map areas to "finish" the game. But if you want to experience all of the story content, 100+ hours if you do a fair amount of side activities. If you do everything it will be longer.

The extra story DLCs I played added nearly 30 hours on top of that, and I still have one story DLC left.

are all the Ubisoft+ games available through PC Game Pass?

Most are. Most include all DLC but there may be exceptions.