Not as good as I'd hoped. I've played all versions of AoE and was excited to see AoE IV in the steam sale but it does not live up to my expectations and is not an improvement on the previous game.
Units take a long time to produce and move slow. Apart from scouts, cavalry is barely faster than infantry. You can't use villagers to herd sheep, the villagers just kill them. Military behaviour is dumb, units prioritise killing buildings close to them rather than buildings that are attacking them or that can produce units. For example my army will happily spend the time to take out lumber and mining camps while being attacked by a fort. Siege units seen to do their own thing. You select where you want them to move but they get distracted on the way and never reach the destination. If your villagers are being attacked it's several clicks to get them to a safe place, even if there's a watch tower right next to them. Because of how slow and dumb units are, games take ages to finish.
I do like the educational aspect of the campaigns with the cut scenes and historical explanations but so far this is the only positive I see in the game, hence the 2 star rating.
To summarise, it's a slow and frustrating game and I wish I'd not wasted the money. Stick with AoE III.