Levels - the clear progression system to guide you through your epic adventure and one of the video games’ defining features.
As players we hardly ever think about level design in games, but I would argue that it is one of the most important aspects. Levels not only allows the player to see their progress, but also allows them to allocate how long they want their play session to be. Because of this, game designers have had to find intuitive ways to keep levels interesting and for appropriate amounts of time.
We have had levels since the early days of gaming, from the castle to castle hopping of Mario to the action packed run and gun shoot-em-up Contra. Most levels in games will reflect the story progression of the game (with some secret/bonus levels thrown in occasionally), and the further the player progresses in levels the further they are in the game. However as games changed over time, designers needed to deviate from the idea that video games needed to be split into discrete sections for a better gameplay and storytelling experience. Valve tied this in Half-Life and Half-Life 2, where there is no explicit level system - although the whole game is linear like most FPSs out there, it had barely any interruptions to the core gameplay. Each chapter transitioned smoothly to the next and you could easily lose hours of your day because the whole experience was so immersive. However, the game did let you save at any time so it gave the player full flexibility on how long they wanted to play.
Over time, as more and more open world RPG games took to the market, the questing system started to go mainstream. Although traditional levels and quests came from completely different backgrounds, recent games have tried combining both and with great success, a great example is the Borderlands series. As mentioned above, FPS games tend to follow a linear story allowing very few deviations to the main plot. In Borderlands however, they have combined all the best bits of RPG and FPS games, including the questing system. Quests can be seen as a set of “mini levels” which the player can choose from. It allows deviations from the main plot and in turn explorations of the world. Although not applicable to every game out there, it lends itself very well to the Borderlands franchise as it helps develop all the quirky characters and the captivating environments.
However all this change is not to say that the traditional system is out of date or boring, I mean Halo 4 was about as linear as you can get but it was still an amazing experience, it’s interesting to observe how it has evolved through the ages and how it might evolve in the future. I’m personally interested to see what else designers have up their sleeves, with all this focus on open world games, maybe we need Valve to come along again to redefine another genre of gaming and show us how it's done… Half-Life 3 perhaps? Please?