I read a review that listed not having things like religion and culture as significant and notable weaknesses of the game; I think that offers some insight into the kind of people who say that it doesn't change the AoW formula much. AoW has always been very much a fast-paced game about war and tactical combat, and in broad strokes, and if you're used to 'combat' in your 4X games meaning a little stack of flavourless statistics moves onto another and hearing some sound effects, I suppose you might consider them all quite similar that way. The details are very, very much more refined than in AoW3, but the broad gist of 'build armies, plunder dungeons, crush enemies' isn't all too different; if you rank things like religion and trade and other such nonsense above good old fashioned killing people in your strategy games, you probably won't enjoy it.
The more enlightened among us recognise that there are many new and interesting ways to shoot, stab, electrocute, incinerate and otherwise slaughter your foes that this is indeed its own game and very much different from the previous AoW games, and that's not even counting a lot of little changes and improvements that make it feel so much smoother to play than AoW3. Alas, not everyone has the refinement to perceive all these details, so I suppose to them the games must seem rather similar.