I would say:
- The build up to war meaning there is no ‘opening moves syndrome’, which I really dislike about A&A.
- The softening of ‘just stack infantry and your more expensive units will never die’ philosophy through things like target selection and air superiority rules.
- The revised rules on blitzing and naval screening forces meaning a single infantry or ship can no longer block an entire fleet or army.
Basically I like the things which take the hard edges off A&As rule set which are an established part of how to play that game but really, a bit s*&t when you actually stop to think about it.
Oh and 4) the revised unit prices for version 3 so that certain unappealing unit types are more likely to be acquired.