I love the fact that they actually decisively ended the series in 2 rather than running the franchise into the ground. The second game was a big step forward in terms of graphics and cutscenes, but the actual gameplay wasn't as fun as the first game. The reduced health and regular lightning using up energy made Cole seem much less powerful than in the first game, and the missions were somewhat repetitive. The craziness of the original (psychic homeless people in trash mecha, anyone?) was nowhere to be seen too.
A prequel where you play as Kessler after he leaves Empire City and develops his powers in different ways might be interesting though. Time manipulation could be a good gameplay mechanic (think Sands of Time, although it's not that applicable to a game like inFamous). It could be a good way to delve into his backstory like Big Boss in Metal Gear Solid 3, and flesh out the First Sons and the original timeline.
A prequel where you play as Kessler after he leaves Empire City and develops his powers in different ways might be interesting though. Time manipulation could be a good gameplay mechanic (think Sands of Time, although it's not that applicable to a game like inFamous). It could be a good way to delve into his backstory like Big Boss in Metal Gear Solid 3, and flesh out the First Sons and the original timeline.