I feel it's necessary to warn you about some things in this game:
***Predator Ranking system is ridiculous. You need to rank up the predator path to unlock the sonic batarang and shock upgrade. You can only do this (mostly) during Predator encounters. Predator encounters are FINITE. What's more, there is one rank that can only be earned on one specific encounter. If you miss that chance the path is completely locked off until new game +
In order to avoid this, from the word go try to get at least one rank per encounter. These require arbitrary tasks and feats to be completed, some of them being a real pain in the ass. The earlier you do them the less stress you'll have in later encounters that are more taxing. Some of the ranks are bullshit and counter intuitive to the path. Predator is all about being unseen and rapid takedowns, but one rank requires you to not use takedowns at all (you can only use strikes, gadgets and beatdowns). Others are really hard for people not too comfortable with Arkhams stealth mechanics (one requires you to not use detective vision and not being seen, which is easier to do in some encounters over others).
***There is a bug related to rankings. Gotham protector requires you at some point to stop a crime a in progress in each area, including Pioneer Bridge. However, Crimes in Progress NEVER OCCUR on the bridge except for one scripted event that happens at the start of the game, long before you could possibly get to the rank in question. There are only a few ways to deal with this: You can either go into new game+ and trigger that event again, glitch the game during a Crime in progress in Sheldon Park OR luck out with a bug that registers another crime in progress elsewhere as the bridge.
***Not sure if this is a bug, but I like to think it is as if it isn't it just means the designers are morons. If you are looking for a thorough play through, including tracking down all of enigmas data packets, you will need to interrogate enigmas data handlers. One of the data handlers doesn't spawn until the post game (when you just free roam and finish things off) and sometimes (especially if you go straight for him after beating the game) he can't be interrogated. Just restart from a previous checkpoint if this happens and try again. If you are diligent you can get most of the data packets that he would've revealed but you can only collect 100% in post game (requires certain events to occur to make one accessible).