The popularity of the "Call of Duty" series puts the franchise in a tough spot creatively, as drastic changes might turn off longtime fans. When "Call of Duty: Black Ops" was released two years ago, game developer Treyarch demonstrated it was willing to take risks by shaking up numerous multiplayer conventions. Fans loved the new features, and the developer has shifted its focus to campaign changes for "Black Ops II," released Tuesday.

Some of these risks pay off, and others are faulty despite their ambition.

A frequent critique of the series revolves around the restricting linearity of its campaigns. "Black Ops II" counters this in two ways: presenting the player with narrative-changing decisions and adding a sandbox, Strike Force missions.

During my six hours with the campaign, I sometimes didn't even realize how my actions had shaped the situations. You are occasionally presented with immediate choices like, "Do you want to kill this guy or not?" but others aren't as overt. As you enter one area near the middle of the campaign, your enemies are desperately attempting to burn evidence of some sort. Depending on how quickly you kill them, you might gain some information that will assist the overall war effort.

Interspersed between the story's chapters are the new Strike Force missions. These are undoubtedly the weakest part of the single-player component. The idea of integrating sandbox stages with real-time strategy elements could have been a great way to shake up the standard gameplay. Instead, these stages are full of frustration as you attempt to control your AI teammates.

If you take these missions out of the equation, the "Black Ops II" campaign is on par with previous entries. Hopping between the 1980s and 2025, it tells the story of the original game's Alex Mason and his son David. Everything moves at a breakneck pace, big set-piece moments punctuate the action, and Raul Menendez proves to be one of the best antagonists in the series.

With the focus on introducing new elements to the campaign, it seems that multiplayer was approached with an "if it ain't broke" mentality. "Black Ops II" gives multiplayer fans countless tweaks and changes to the formula. New league matches are tailored to the e-sports community. But for shooter fans who don't require as deep of a dive, "Black Ops II's" multiplayer may feel like more of the same.

Despite some frustrations, "Black Ops II" is another massive, polished entry in a series that shows no signs of slowing down.