There's a simple flowchart for that:
-
never touched a Bethesda game before = try it and see if you enjoy it
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enjoyed another Bethesda game before = see above
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didn't enjoy your experience with a Bethesda game before = probably safe to skip it
The only caveat is if you're one of those "RPGs must have choice and consequence" types. For that sort they'll sing the praises of something like New Vegas while vehemently shitting on Fallout 3 and 4 as if enjoyment of one title must be mutually exclusive from others.