You haven't played Mass Effect?? YES, YES, YES!. Umm... my vote is yes it's worth revisiting. It has it's highs and lows, but overall the first 3 mass effects are probably my favorite game series of all times. If you've never played a mass effect before (kinda confused by what you mean by revisit, so not 100% sure if you've played it before, but if you have also not sure why are you asking..) you should run though all 3 of the original ME trilogy. The first is a little bit rough of a game at times, they were still figuring out the series, second game may be my flat out favorite game ever made top to bottom, and I love the third until the last 5 minutes. So far I could take or leave the 4th game Andromeda, it's unrelated to ME1-3, wasn't bad, just wasn't anything special to me.
FO4 most people love, i'm really the outlier on it. I really enjoyed playing with it until I got too far in the main story, then I started to have "issues" because I didn't really like what I was being told to do by the groups I had chosen to side with. It's a top notch game, so if you like Fallout, go for it, it's well done.