A little background.
For some it's strange to think of a time in which CoD wasn't a house hold name. A time when it wasn't a huge juggernaut that smashed its own records each year, and drew hatred from gamers labeling it "everything that's evil in the gaming industry". A time when all the frat boys played Halo, or Madden. Indeed CoD was once a somewhat low key IP that really centralized around World War 2... back when it was a viable setting. It was a franchise really just jogging along in the waning shadow that was Halo. It wasn't until CoD4 that the series really hit home with many gamers. The idea of leveling in a shooter seems common today, as it's a common technique. However CoD4 was really the game that started that trend. The idea of leveling was very addicting, as it had that MMO type feel. Coupled with a somewhat balanced game, and some innovative features like perks, and killstreaks it would start it's climb into the spotlight. World at War was released with Treyarch feeling the need to continue this World War 2 setting and it was somewhat of a flop. Treyarch has always been terrible at balancing weapons as their SMGs tend to outshine most other classes, especially in an era when most rifles were semi auto, or bolt action. Most fans were saddened by this step back and were looking towards the horizon for MW2.
Modern Warfare 2... the only midnight release I've ever gone to, and really is the reason I'll never go to another. The game promised much and introduced easily the most subtle feature that would grab onto the collars of the players and never let go.
Audio and Visual Cues:
This may seem stupid, or irrelevant, but it is actually a powerful tactic to keep players interested. Watching the progression in the CoD series, and also looking at the difference between BF3 and Bad Company 2, I've noticed these visual and audio cues that play when you level, complete a challenge, or unlock a weapon/attachment/perk. It's like how casinos have that overload of sounds, and sights. When someone wins there is a flashing of lights and a sound that plays to announce that person won. Whether it's you, or the person next to you that attack on your senses can be a determining factor as to whether you play again or not. The same idea has been implemented into many popular games.
Skyrim is no exception. When you leveled in Morrowind or Oblivion you were greeted with a "You leveled", it wasn't very significant, nor was it flashy. However in Skyrim you're greeted with a powerful choir who fit the Nordic feel of the game, you see that level bar progress until it fills it completely. The bar then flashes and you're told that you leveled up. This little greeting is then look forward to as you're being rewarded for leveling, and even by progressing.
Perks:
While some games try to cover up their "perks" with a different name Skyrim doesn't sugar coat it. These are perks, they're more interactive, they have different components, different ideas. It's no longer random points increasing with little, to no visual representation. It's now a perk that you can select, a perk that explain what it does and allows for advancement within the skill tree. While perks are more of a blending between conventional skill trees, and perks, they allow for a customizing of the character similar to CoD. In CoD you could extensively be a run and gunner, stealth, or tactical player. Not unlike the different RPG archetypes that Skyrim has.
Movie Styled story:
The way that games are going they strive to have that "movie feel". While some games like CoD fill you with over the top, dude bro moments. Others try to take a more traditional approach like Uncharted. Either way many games want you to have that feeling of "epicness", and want you to always be engaged. Skyrim is the same way, the story is much more fast paced, allowing for small pockets of down time (like climbing up 7,000 steps) that let you soak in the world that Bethesda has created. When you do catch your breath you're funneled along again, fighting more dragons, stopping civil wars, and saving the princess.
While I'm not arguing that CoD is the direct cause of these changes. There is something to be said about the influence CoD has on the entire market, even on games outside its own genre.
