Fallout 4 is on sale.
Is it worth getting?
And more specifically is the Game of the Year Edition a good buy to get the addons?
Fallout 4 is a poor Fallout game, suffers from a weak story, and is only good in comparison to Fallout 3 (as opposed to the superior New Vegas). It does have fun game play though and I enjoyed base building, so it's not an entire wash.
Add-ons:
Automatron - Lets you build robot settlers and modify existing robot followers, as well a new robot follower and a short storyline about THE MECHANIST and her robot army. Fun and robot settlers are highly useful.
Far Harbor - A new island to explore with cool story. Bring Nick with you, this story is his as much as yours.
Nuka-World - Another new location to explore with lots of new weapons and introduces the ability to side with the Raiders in their takeover of the Commonwealth. If that's your style, you'll have a lot of fun, but if you don't want to play raider than this dlc loses a lot of it's appeal and special perks.
Contraptions and Wasteland Workshop - This adds more stuff to the base building system, including lots of new traps and the aiblity to construct assembly lines to produce things like bullets. Useful, but nothing amazing.
Vault-Tec Workshop - Get a small storyline about constructing a vault inside a mountain, as well as tons of vault-tec inspired parts to play with. Nothing amazing here though.
Honestly? A lot of what I liked about Fallout 4 is found in Fallout 76 these days and Fallout 76 just keeps improving and improving. Unless you need the companions and story of Fallout 4, I would just skip to 76 at this point.