It really depends what is your cup of coffee. I would personally say AoD to be alot beter than HoI2DD\ArmA due some of the fixes:
1. Megasuperstack-masscombat is no longer effective way to steamroll everything in sight.
2. Battles are not based on sword and shield warfare, large battles especially can take notable amount of time, even more so in 'poor' terrain. Makes air support quite handy and air parity, superiority and supremacy have bit more important roles to some degree. Zergrushes are also - as noted - not that useful anymore.
3. Air and naval combat are also bit more reasonable. Ships E.G. needs to actually spot eachother before they can fire and they can no longer close in over 100km+ in one single hour no matter what you try (even without the known CVL exploit in ArmA it was possible to close in over 180km range in just one hour) among other things. Fleet beaming and DD-zergs are also eliminated in general.
4. AI is improved. While it still tends to do some silly stuff it used to do in HoI2 it actually knows how to avoid most obvious encirclements and such.
5. Brigades are actually useful. You could say that in HoI2 never use brigades (unless for gameplay or historical flavour), while in AoD use always brigades if possible.
6. Logistics are handled more reasonably. Also, if your puppet is incapable of supplying your own army it actually starts using your own supply lines rather than the puppet's.
7. Money is more important when it comes to nation's basics.
8. There's alot of new features. Refer to developer diary archive for some of them and some of the changes as found in here:
http://forum.paradoxplaza.com/forum/showthread.php?t=436808
Only thing one could gripe about is that some truly funny things you could do in HoI2 (E.G. Anschluss of everybody) are far more difficult - if not close to impossible and lack of polish here and there, such as missing pictures or so.
It certainly doesn't reinvent the wheel but instead improves it to a whole new level.
