It was free to play. But it didn't hold a candle to Team Fortress, Call of Duty, or even Tribes in terms of overall player count. The project was eventually abandoned when Pentagon officials realized they could just send kick-backs to EA executives in order to inject their propaganda into a more popular franchise.
Now US Army and Navy sponsorship of tournaments is routine, streamers regularly get promoted based on their military affiliations, and native advertising has ramped up substantially.
But it didn’t hold a candle to Team Fortress, Call of Duty, or even Tribes in terms of overall player count.
In terms of player count, no. But mechanics and graphics? They were pretty freaking good.
Although one pretty ridiculous thing was that one would never play as "the enemy." You're always on the side of the US Army, obviously, and the enemies are vaguely mid-eastern people dressed very stereotypically, yelling. But if your friend was on that enemy team, they'd see themselves as a US soldier and you as a somewhat racist terrorist stereotype. And the guns work like that too; you start of with an M16 or whatever your role might be, but when the enemy kills you, they'll pick up an AK with a drum magazine. Weirdly the guns had different mechanics, so which ones was the game using at what times?
Anyways, thought to mention. I played Tactical Ops mostly at that time (having had stopped CS when the annoying 1.6 steam update came), but with one friend we did AA. Always on American servers, playing with like 190 ping. (And yes, if it's a steady ping, you can actually get used to it and hit things. Well even.)