Genji doesn't play like any other hero in the game. There isn't much overlap between any two heroes in terms of gameplay style and strengths/weaknesses, but Genji is by far the greatest outlier. No other hero rewards smart positioning, on the fly thinking, agility, and precise aim like he does. Similarly, few other heroes have such a high skill floor AND skill ceiling. When you get in the groove with him, you feel like a fucking ninja, it's a lot of fun.
For the record, I don't main Genji despite my avatar, and I haven't played him seriously since his nerf, but I have probably over 30 hours on him and they were some of my most enjoyable times in the game.