Fallout 1, Fallout 2, Fallout Tactics, and Fallout 3.
This series has a long and rich history and numerous followers.
I personally loved the Fallout Tactics. However the Fallout Turn Based Strategy is what kept me engaged through Fallout 1 and 2.
Don't forget Fallout New Vegas, which was released after Fallout 3 so I really don't know why they're calling the next game Fallout 4 instead of Fallout 5. Fallout Tactics was interesting and I also enjoyed Fallout: Brotherhood of Steel for the PS2. That all being said, I'm really looking forward to playing Fallout 4. Does anyone else play the games for months yet never actually finish the main story? I get easily sidetracked, so sandboxes rarely get completed by me.