I have played this came several times. And even someone who knows Arkham Asylum could answer your questions but mujahid does not seem to be into it. Anyway, in arkham city riddler challenges have a couple of uses.
One of them is that it is sometimes fun trying to get through the puzzles and get them. Another is that it increases your experience by 200xp. You can also get xp from fighting.
This only gives it in a faster rate. Each time your xp reaches a certain number you can have an upgrade. Without upgrades certain parts of the game could be very hard, esp if you r playing for the first time.
Certain upgrades are also needed for some of the trophies. Another use is to capture the riddler. Each time you solve a percentage of challenges he would give you the hint of where a hostage is.
You need to then rescue hostage and a riddle that he provides. He would then give you the next hostage location. Finally you will be given the riddler's location.
I know this part would be a little confusing, but just start doing the challenges and you'll get the hang of it. It all starts when the riddler invites you to the church. Just keep your ears open for anyone saying anything about the church (after the top of it blows up).
When you hear something about it, go straight to the church and you'll know what next. The outside challenges don't effect the main story except they may give you some practice. These challenges are mainly to compete online with other players.
You can login to your windows live ID and your scores go online as you play these challenges (i never tried it). You can also simply try achieveing the mentioned challenges (in case of the fights you need to achieve the target points, in case of the prodator modes, you need to use the mentioned techniques). You don't need to solve all the challenges.
Once you have all the upgrades and have captured the riddler solving the remaining challenges is almost pointless. You only get a trophy for it and its not worth it. Another challenge you don't need to completly complete is the "Augmented Reality training".
While doing this challenge, you would get "the grappono boost" which makes things much easier and is needed to get some of the thropies. Once you get this boost, playing the "Augmented Reality training" is again almost pointless as it'll just give you yet another trophy, and since it gets really hard its not worth it. You can always refer to the net to find out how to get a perticular trophy.
You may also like to know that once you have completed the main story, you can play the came wearing a bunch of other costumes (provided you have purchased and installed the DLC) and you can unlock the "new game plus mode". In this mode, you can play the whole story again with all the upgrades you already have and all gadgets you already have. It is totally worth playing this.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.