Songlist Info:
54 arcade songs
26 revival songs
10 console exclusives
The customization features are back, and now the song select music can be customized as well. I will also state that there is now a Pop'N version of the IIDX interface which I personally consider the most disturbing thing I have ever seen in my life.

Also, in a surprising development this release has a timing offset option which surprised the hell out of me. The actual timing of the game is later than most of the prior release, but it's not as bad as 3rd Style thankfully. From what I've seen though, the timing offset itself was intended to fix the issues with more problematic TVs, so the increment is higher than just a few milliseconds to say the least.
The rival system has also been brought back, and along with it there is rival data for approximately 4,000 Japanese arcade players (Plus data for 8 of the 10 Top Ranker Tournament Finalists), which is a nice touch, but due to the fact that the arcade's timing windows is substansially smaller than the console version this should only be used as a guideline for reaching a higher EX score and not as an actual measurement of skill against other players.
As for the actual gameplay, personally I'll say that this is the hardest release that I have played hands down. Most of the newer players might actually be scared away from this particular release cause of how hard it is. Honestly, I like the overall increase in difficulty as it is a reflection of how the series has evolved and also reflects the usage of the ratings system of 1 to 12 for difficulty.
Overall, it's a very well done release and I recommend it to all IIDX players aside from beginners. In my case, my social life will most likely become completely nonexistant.