Saints Row 1 is pretty pointless. It's a straight GTA clone that isn't as good.
Saints Row 2 isn't too bad, though it's pretty dated now. It's still a GTA clone but it has a lot of silliness as well. I personally think this Saints Row had the best combination of the two. It also had a lot of quests that I remember till this day (e.g: failing to rescue your friend from torture, the weed jamaican car scene, etc.)
Saints Row 3 is pretty forgettable and also very short. The cast of characters is pretty cool though, but other than that it's not particularly impressive. Also they did that whole "let's kill the interesting villain straight off, then replace him with an unlikable moron".
Saints Row 4 is very fun but I don't think it's really an open world game any more. The plot is pretty short, concise, and it doesn't really expand on any open world things. I would treat it more like an action packed third person shooter like Uncharted rather than like GTA. In that sense it's very good, but does require knowledge of the previous games to kinda understand.
P.s: I used to use the male voice 1 for the series but when I replayed them I went female voice 1 and never looked back. She's so, so, sooooooooooooooooooooo much better and has so much personality. I can't see the boss as anyone else.