These games are essentially âopen world.â That world has grown since the first game came out. The typical usual characters are in them, perhaps with some surprises. There is a lot to do, like collecting Riddler trophies. Each installment in the series seems to have...

It's one of the best series I've played. The fact that they got back the voice talent from the animated series (Conroy and Hamil, who you mentioned, especially) adds so much to the experience and kinda takes you back to those cartoons. But this ain't a cartoon. It deals with some pretty heavy stuff.
You're right, they've fixed nearly all the issues that plagued the game at launch. It still has some performance issues but with a godly or demi-godly rig, you will barely notice them.
I didn't like the reliance on the Batmobile for so much of the game, and the Riddler trophies are fun but I thought there were too many of them, and I never did the Riddler's final fight because it requires collecting all of them. But those are really the only complaints I have. It's one of the first games I retried on my new(ish) PC to see how much more performance I could squeeze out. Quite a bit, as it turns out. And I enjoyed playing a few hours again with a new coat of paint.
I agree about Riddler collectibles. I'm still collecting them, I have less than 40 left I believe. Some are frustrating, but some are fun. It's kind of tedious.
Oh, did you play w/ a controller or keyboard & mouse? I can't imagine playing it with the latter. As I talked to a friend about it, I mentioned how it reminds me of GTAV, but he said it also sounds like Assassin's Creed. That seems about right, although I've really only played the first one.
I love Batman and need to put time into these games. I hear so many good things about them.
I'd say there's some obvious inspiration from GTA for the drive-to-the-mission sections, but anything with cars is taking inspiration from them these days. Asscreed is also a big influence, especially with the stealth focus. But then so is Devil May Cry, maybe God of War... it pulls a lot of good stuff from a lot of good things, as does most everything, but really it's very original in the way it approaches things.
I played with a controller, but quickly swapped to a KB/M whenever the Batmobile combat mode was needed, since that plays mostly like an FPS (surprisingly). I agree though, I couldn't imagine KB/M for a third-person action game.