Here's a few nuggets I noticed and said "yay!":

Old Man Willow makes you "tired".

In Book 1, Frodo is mentioned as Mr. Underhill.

You feel dread anytime you're around Frodo in Rivendell since he has the One Ring.

Trolls are found out in the open only at night (they hide in groves/shaded areas during daytime).

You can see flocks of crows/ravens(?) scouting through the skies in the distance at times (High Graphics I think).

The ruins south of Breeland actually does run from the Old Forest to Midgewater Marshes. It was mentioned in passing in one of the books and I happened to be playing around there that day and decided to trace how far the Ruins ran.