Stellar multiplayer action makes up for a lackluster campaign.
Upon booting up either the multiplayer or campaign modes of Halo 4, the first thing you'll notice is the improved presentation of the game. This is easily one of the Xbox 360's best looking games, and it's certainly one of the top contenders of this generation. The sound has also been improved across the board, especially those associated with weapons, which now sound incredibly powerful and deadly.
The multiplayer is the primary reason to buy Halo 4. I was very skeptical of 343's decision to go with a more "Call of Duty" style multiplayer with custom loadouts and unlockable upgrades. Luckily, unlocking these upgrades isn't overly difficult and the overall presence of custom loadouts doesn't change that Halo feel of the gameplay. Unlocking new armor sets is also fun, though the design of the player models often makes it difficult to see the detail in these armor sets. Most players end of looking like robots rather than soldiers. The arsenal of weapons is one of the most balanced and fun of all the Halo games, though the worst are considerably moreso than in past games.
My major gripe with the multiplayer is with the map selection. Halo games under Bungie had consistently good quality in their maps. For every less-than-exciting map like Halo 3's Isolation, there were excellent designs like The Pit, Guardian, and Sandtrap. Halo 4's roster of maps range from the poorly designed Meltdown to the slightly above average Exile. Most of the maps are average or slightly below, making up one of the most unexciting map selections in the franchise.
The episodic co-op mode, Spartan Ops, is a great idea in concept, but fails in implementation. Many of the mission environments are recycled either from the main campaign or from previous Spartan Ops missions. Most of these missions also devolve down to basic "run down the path and kill all the bad guys" objectives. This is especially unfortunate because the episodic nature lends itself to being able to have a great variety in mission structure.
Finally, we come to the main campaign, the return of Master Chief, which has been given a great deal of coverage and importance in the game. So how did it actually turn out?... Meh. The campaign certainly benefits from all the updates made to the gameplay as well as the higher quality presentation. The pre-rendered cutscenes are absolutely gorgeous, and the motion capture and voice acting is superb as well. Unfortunately, the setting of a Forerunner world makes for a lot of bland environments. For every 10 minutes in a beautiful outdoor environment, you spend 20 minutes trudging through halls of Forerunner gray, blue, and orange, and the enemies follow the same color scheme. The excellent graphics are wasted on these boring environments.
For the plot, I find Halo 4's campaign to be the worst in the series. First and foremost, the villain is bland. The Didact is a re-awakened Forerunner and should therefore be incredibly exciting. Unless you've read the Halo novels, it's never made completely clear who the Didact is or what his motivations are beyond "I don't like humanity." I've heard this is fleshed out more in the novels, but the games are the main form of storytelling for this universe. Reading the offshoot literature shouldn't be a requirement for understanding the story. The plot also suffers from subpar pacing. The campaign starts off right, ratcheting up the intensity to start the game, and then settling back a little to let you take in the beautiful landscape of the Forerunner planet. But then it never rises again. The pace stays on a mild, safe pace through almost every mission, the only exception being an exciting vehicle mission near the end.
So, with such a lackluster campaign, why do I give the overall game a 9.0? Because the gameplay is just that good. Playing the game feels fantastic no matter what game mode you're in.
Is Halo 4 the new benchmark for the series? It depends on what you like. For the single-player campaigns, you'll probably prefer those of Halo 3 or Halo: Reach. If you want the most balanced and fun multiplayer, Halo 4 should be your choice.