Wikipedia - The Age of Empires series has been a commercial success, selling over 25 million copies. Critics have credited part of the success of the series to its historical theme and fair play; the artificial intelligence (AI) players have fewer advantages than in many of the series’ competitors.
If it is true, AOEIV is doing poorly and the player number is too low for such a high sales number.
People are definitely disappointed with the art direction, biomes, AI, and size of units vs buildings etc. More than 95% of players have already abandoned the game, and only as few as 5% are currently playing. I would find it a failure of a game.
The sales can be high and a success.
But it couldn’t; satisfy players and their expectations vs reality…