So, let's talk first person shooters. Specifically, console first person shooters. When you do talk about console fps games, there are two heavyweights that must be mentioned- Halo and Call of Duty. And it's interesting that these are the two juggernauts of the genre, because they are great examples of the varied approaches of the genre, as well as features that are generally accepted as great ideas. For example, Halo and Call of Duty both have health that regenerates when not under attack- Halo was such a trendsetter that regenerating health is often called "Halo health". Both also share the two-weapons-on-hand system that Halo made popular. But from there, they diverge, significantly.
With its dual-wielding, bunny hopping, and slow movement speed, Halo is, surprisingly, more like a traditional fragfest shooter, when you get down to it. It has powerups, weapons scattered about the map, and run-and-gun action. Halo was revolutionary, but it didn't create a new style of game, not at all. It took the old recipe of Doom, Quake 3, and Unreal Tournament, and modernized it. Sure, the mega-hardcore still prefer health bars, but Halo health rewards smart, tactical play over map memorization. And the two-weapon system was just the only way to handle weapons practically on a console. On the PC, you have the whole numbers row to play with, but on the console, you do not have such a resource. In multiplayer, you need to be able to select the weapon you want quickly and efficiently. Thus, the two weapon system.
The problem with Halo, in my mind, is that it draws all the elements of old fragfests without nailing the most important one- chaos. Sure, any time you have 16 players going at it, there is going to be some chaos, but games like Unreal Tournament nailed it by having superior control with fast movement and great jumping ability, and having weapons that were devastating and wild. Remember Unreal Tournament's rocket launcher? The one that could chamber five rockets and launch them all at once? There really is no Halo equivalent to that. Unreal Tournament was not designed for genuine competitive play. It wasn't designed for pro tours. Halo was, and yet it tries to be a fragfest at the same time. It is in this that it truly fails.
Compare this to Call of Duty, which can hardly be said to be the same series it started as. At first, it was basically like Medal of Honor, but better- a World War 2 shooter with a health bar, plenty of weapons, all that jazz. But the things that made it really special, even then, are still a constant- first, no weapons scattered across the map. What you start with is what you stick with. Because of this, you also had much less downtime after respawning- you didn't need to run to this area to get a good gun, then run to that one to get body armor, you could just get into position and start shooting. The other innovation- let's be clear, I know other games did these first, but CoD made them popular- was iron sights. The concept that with any weapon, not just a sniper rifle, you actually had to stop and aim to have any kind of accuracy, was novel and genre-changing.
For years, we'd been content playing as a superhuman who could snipe enemies from a mile away with a pistol without even lifting it to his eye to take aim. Suddenly, we had to play like real human beings- balancing mobility, accurracy, and cover as best we could in order to stay alive. Call of Duty 2 added Halo health and the two-weapon system, and boom, you had the recipe for fantastic, amazing gameplay. Then you add Call of Duty 4's class system, and it's no wonder that many (myself included) consider it the best console FPS this generation (because, come on, even if it was better than Perfect Dark or Goldeneye, I could never bring myself to admit it).
And what does all this teach us? Well, basically, that reality can be fun, that it doesn't have to hold back a game. Similarly, it teaches us that some things, some realistic things that we cling to because we're just so used to the idea... really just don't need to be in games. Like health bars- they have their place, but there are not a lot of games where I feel that regenerating health wouldn't serve better. FPSes are moving forward, and let's hope they continue to do so.