It would be important to think about defiition of Fallout.
For me.
1. Quest based RPG
One of most improtant thing of Fallout. without quest, there's no reason to stick with Fallout: Jagged aliance has better combat. but for quest there's too little game which has better quests than Fallout
2. Post apocalypse
3. Rebuild of civilization
Not only destruction but also people find how to survive, how to rebuild and how to begin again. This makes me impressed. PA is meanigful because of this.
4.SPECIAL and skills
The methods to solve the situation(quest) not just doing stupid minigame or only for combat.
5.Perks
6. Ending
Fallouts(not for 3 I guess? and don't know about POS) has awsome endings that shows your journy chages the world.
Without these 6, I can't call fake fallout a Fallout.
For me.
1. Quest based RPG
One of most improtant thing of Fallout. without quest, there's no reason to stick with Fallout: Jagged aliance has better combat. but for quest there's too little game which has better quests than Fallout
2. Post apocalypse

3. Rebuild of civilization
Not only destruction but also people find how to survive, how to rebuild and how to begin again. This makes me impressed. PA is meanigful because of this.
4.SPECIAL and skills
The methods to solve the situation(quest) not just doing stupid minigame or only for combat.
5.Perks
6. Ending
Fallouts(not for 3 I guess? and don't know about POS) has awsome endings that shows your journy chages the world.
Without these 6, I can't call fake fallout a Fallout.