By some metrics, Call of Duty: Advanced Warfare might be the biggest entertainment release of the year -- emphasis on might -- but it's not likely to be 2014's most profitable game. That title's probably going to go to League of Legends, the online battle arena game that makes roughly $1.7 million per day.

In fact, League of Legends is so far ahead of the pack in terms of revenue that only a couple of other games even come close. One of those is Clash of Clans, Supercell's ubiquitous mobile strategy title. Well, Activision's noticed, and while they haven't transformed Call of Duty into a MOBA (yet), they're certainly interested in capturing some of that freemium-driven cash. Enter Call of Duty: Heroes, a "free to play, 3D combat strategy game" that takes Clash of Clans' basic gameplay and adds Call of Duty-specific weapons, characters, and gameplay features.

In Call of Duty: Heroes, players transform a base from a "small outpost" into a towering fortress by deploying Call of Duty fixtures like sentry guns, SAM turrets, and over thirty types of upgradable buildings. Call of Duty: Heroes also allows players to control five classic heroes from games like Call of Duty: Modern Warfare and Call of Duty: Black Ops II. Captain Price, Soap McTavish, and Mike Harper are all here, each possessing unique killstreak abilities that wreak havoc on their foes.

Call of Duty: Heroes does have a single player campaign, but the game's real draw is its multiplayer. Much like the "clans" in Clash of Clans, players can join up to 25 other players to form powerful "Alliances." Friends can help one another by sharing troops and supplies, while one-on-one battles against other players provide most of Call of Duty: Heroes' actual challenge.

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Call of Duty: Heroes also includes its own spin on the series' "Survival Mode," sending wave after wave of computer-controlled enemies towards players' bases. Survive the increasingly difficult attacks, and players will earn experience and in-game currency that can be used to upgrade weapons and characters.

And of course, while the game is technically free, the game is filled with micro-transactions. Dedicated players can drop anywhere from a few bucks to $125 to make sure their base is the best it can be.

That's a substantial amount of cash, and given the similarities to Clash of Clans -- killstreaks notwithstanding -- it's hard to view Call of Duty: Heroes as much more than a simple cash-grab. Still, for Call of Duty fans, maybe the chance to unite the franchise's most iconic heroes is worth the money. Time will tell.

Call of Duty: Heroes is out now for iOS. It's coming "soon" to Android and Windows 8 devices.