I'd say the only thing the previous games do better is that, yeah, they feel a bit more fleshed out, even if that more fleshed out content is of a lower quality than the somewhat less fleshed out Second Son content. But in regards to that... you have to take into consideration that inFamous 1 was released over 2,5 years after PS3's launch while Second Son is a launch era-ish title. Near launch titles are pretty much always a bit rushed and/or light on content, especially in comparison to some late-gen predecessors that benefit from years of experience & work on a single platform.
Other than that? Most importantly, the gameplay is vastly superior in Second Son. It's just so fluid & fun. Sure, 1 power in Second Son might not quite compare to all the options you had with electricity, but when combined all the different powers have things differentiating them from each other in movement AND combat abilities, which makes using them feel somewhat different. Sure, there are grenades in more than one power, but they are used completely differently. Smoke power's grenades suffocate enemies so that you can go in for melee kills or KOs while Neon power's grenades are meant to give you better opportunities for sniping action. That changes the dynamic of the battles enough so that one grenade doesn't really feel like the other in context of all the battles.
In addition to that, the acting is way better, the dialogue flows much better and the characters themselves are better in many ways, even if they end up being a bit underutilized & -developed. I'd actually want to have Fetch & Eugene in future games, while I have had enough of most of inFamous 1 & 2's characters in the previous games. I don't really need to see more of Kuo or Nix, but I wouldn't mind if Eugene and/or Fetch were in Second Son 2, if Sucker Punch decides to continue the franchise.
All-in-all, inFamous Second Son is way more fun to play and its characters are more enjoyable to follow, but the only problem is that some of it isn't as well fleshed out as in the previous games. Still, I'd probably rather return to Second Son than 1 or 2 any day of the week, it's just that much more fun to play.