They both have:

• Magical hive mind disease
• Strange, deadly weather
• Crazy, unique mutant/magic animals
• Annoying flying enemies
• A large group of people that fucking disappeared, leaving strange and advanced technology behind
• People that sound like chain smokers
• Large Weapon Variety
• Large part of the plot is curing/stopping said magic disease
• Wide variety of distinct regions that are somewhat cordoned off from each other
• Arguably the Best in their series
• Multiple diseases of varying strengths
• Lots of mines
• Wide variety of enemies
• Cult areas with strange architecture
• An entire area covered in ash with lots of hills and mountains
• A large area that runs down the middle and is fairly mountainous
• Try to tell a serious story while still retaining fantasy elements
• A marshy area in the northeast
• Giant bugs

On top of all that, Fallout 76 is less buggy, obviously looks better, is constantly getting updates and tweaks (the most popular nexus mods are literally features now) has a more freeform story (you can ignore parts of the plot if you want, just like with new vegas) and is literally multiplayer. Plus there's the base building, the camp building, the MODIFYING your weapons, the seasonal events, and most of all, the fact it isn't 20 fucking years old with an rtd combat system.

Morrowind Spiritual Successor confirmed.