The pilum is a thing unto itself. I wouldn't call it a javelin, maybe a "heavy javelin" (as wikipedia calls it) if you really want.
The latin for a regular javelin is iaculum and it's smaller than a pilum and purely for throwing. Romans used iacula extensively on their lighter troops...
Like: The general streamlining of play and rules.
Dislike: One spell per day at higher spell levels. If I'm a level 20 wizard, deadlier than quite a lot of dragons (per CR), I want to unload.
Intrigued that nobody is mentioning: Inspiration, which nudges D&D a bit towards them new-fangled...
I remember an ENWorld thread many years ago, I think it was started by a publisher, which was called something like "why don't you buy published adventures?" And by far the most common response was "because I can't fit them into my campaign". Published adventures, at least if you read that...
And in D&D we can have magical authentication of credit. Sendings to validate that IOU, and so on.
Surely this is a perfect business for the church of Waukeen, or whoever has that porfolio.
I am waiting for Mostin to gate in on Eadric + Shomai at an awkward moment, deploy disjunctions and a Gu, and then say "oh, er, sorry, I didn't realise you were, err, umm..."
If you don't mind drinking two fingers of whiskey and squinting, you might just about squeeze GURPS Cliffhangers plus the free lite rules in under that. After all, if you get the free PDF version of the lite rules, it's only one book. ;) [But I must admit that I don't think the Lite rules work...
I bought a book like FRCS specifically to save me the work of making stuff up. Why would I go changing it?
If I wanted to create setting details for myself, I'd use Greyhawk.