tl;dr: Unequivocally the best RTS game on the market. The central gameplay loop is unique enough between factions to remain interesting for outrageous amounts of time, while being approachable/arcadey enough that the average gamer can pick it up easily enough.

Graphically there are some hiccups such as lighting being too bright in snow, but overall this game is absolutely gorgeous.
Content-wise there is enough to keep even the pickiest player interested. With the addition of Immortal Empires as playable for all owners of this edition, you can experience content from all 3 games and see first hand how well they've done with balancing. Older factions may not be as polished nor have as many mechanics as newer ones, but the overall balance is so well done that most players will struggle to name more than 2 or 3 factions out of the 24 available factions that need a touch-up.
There are hundreds of mods available on the mod workshop, and even if you only explore the more polished ones you could easily double your playtime with what players have posted.
Multiplayer is fantastic. I don't personally recommend doing a campaign with more than 1 or 2 people just because waiting on 7+ battles every single turn in your 8-person coop is a bit boring, but if you did decide to do a massive multiplayer campaign like that the game handles it flawlessly. I can count on 1 hand the number of multiplayer errors I've experienced, and since the game autosaves every turn they aren't that big of an issue.

tl;dr: Unequivocally the best RTS game on the market. The central gameplay loop is unique enough between factions to remain interesting for outrageous amounts of time, while being approachable/arcadey enough that the average gamer can pick it up easily enough. Graphically there are some hiccups such as lighting being too bright in snow, but overall this game is absolutely gorgeous. Content-wise there is enough to keep even the pickiest player interested. With the addition of Immortal Empires as playable for all owners of this edition, you can experience content from all 3 games and see first hand how well they've done with balancing. Older factions may not be as polished nor have as many mechanics as newer ones, but the overall balance is so well done that most players will struggle to name more than 2 or 3 factions out of the 24 available factions that need a touch-up. There are hundreds of mods available on the mod workshop, and even if you only explore the more polished ones you could easily double your playtime with what players have posted. Multiplayer is fantastic. I don't personally recommend doing a campaign with more than 1 or 2 people just because waiting on 7+ battles every single turn in your 8-person coop is a bit boring, but if you did decide to do a massive multiplayer campaign like that the game handles it flawlessly. I can count on 1 hand the number of multiplayer errors I've experienced, and since the game autosaves every turn they aren't that big of an issue.