The 3rd edition has a cleaner format. It hasn't been crowded with irrelevent pictures and other distractions from the content. It also suffers less from political correctness, although the exclusion of Caesar could be taken as an earlier form of political correctness.
On the other hand, the newer editions have reading passages for every chapter. The vocabulary is to be thouroughly learnt, whereas the 3rd had a separate "recognition" list to be learnt less thouroughly.
It's also a lot easier to find an answer key for the newer editions.