There have also recently been new army books for Orcs, Empire
(edit: I'd forgotten that one) and High Elves, as well as Wood Elves, Dwarves and Ogres before that (can't think of any more).
So depending on what you play, and how long you've been away, some armies may have changed more than others.
As I recall, the only 'thing' that was definitively lost in 7th ed was some Brettonian magic item; but there have been enough changes to the general way things work that I'd advise you to get the new book.
Don't know of anyone still playing 5th ed. Did you mean 6th ed? Put out a call for players in your area, that's my advice.