LEGO Batman 3: Beyond Gotham was the first game I ever completed to 100% and also some of the most fun I ever had playing a game. I originally bought this game to play with my kids but quickly found myself staying up well after they went to sleep chasing additional achievements. The gameplay was more enjoyable, and seemed more refined, than previous LEGO games. Honestly besides the various quests/challenges that involved vehicles I never got overly frustrated with any of the mechanics. The story was fun and the extra characters they added made me want to keep playing until I unlocked everything.
Time to complete if you are just going for achievements should be around 25 hours. Since I was enjoying the game so much with my kids I didn’t rush and completed it in roughly 66 hours.
Difficulty rating would be a 2 out of 5. It is actually pretty close to a 1 but some of the vehicle achievements take a little getting used to and some skill.
Overall I would give the game 5 out of 5 stars and is a must if you have younger children or are a Batman fan.