I also hope someone will give people the ability to go back and explore the wasteland and do side quests after finishing the main story.
While I can't argue with you other points because well they need fixing.
However main quest finishing and ending the game is neither a bug nor a glitch. It's a feature.
You need to either save before the final quest (like the pop-up says) or start a new character and play it completely differently than the first time.
Either way, welcome.