As the result of a write-up of the ranger "design goals" on the Wizards of the Coast website, there has been a lot of discussion of what a ranger is and what it should be. I figured I'd chime in with an opinion because rangers are the second most common class I play (the first being rogues), and I've played a ranger on more than one occasion in every edition they've existed in in D&D. I felt it necessary to come to their defense.
Before I continue, let's have a little history on the ranger as a class... The ranger existed as a core class as far back as AD&D 1st Edition (it was technically absent the in Basic edition; support for playing a ranger in the Basic edition was provided in Dragon Magazine), and since then it has been a constant presence in the D&D class list despite going through some seriously radical changes in each edition: he went from having favored enemies to quarry damage, his spellcasting power source wavered between primal (druid), arcane and divine, and at one point rangers were even limited to the races and alignments they could be (in 1E, they were forced to be of good alignment).
But with the coming of "DnD Next" many are asking whether the ranger should be its own class at all. Logically, it's very possible that the ranger could be a subset of the fighter or rogue and made more ranger-like through the use of themes. After all, a ranger is arguably not much different than a fighter but with an affinity to natural environments.
Several arguments have been made regarding this, and quite a few of them actually make a very good case and could work quite well as a theme... but a problem exists: the ranger class has a history. It doesn't really matter if a ranger-like PC can be better designed with themes, background, feats or a lot of flavor text; the ranger has to exist as a class because it's been that way for over thirty years. If a player sits down at a game and says "I want to play a ranger," he can't be told "there isn't one" or "here's to play a character that is kind of like a ranger... only not."
In my opinion, there are certain aspects that have become required elements of D&D. Some more than others, of course; players will always have the six attributes, they will always have some sort of AC defense (how it is calculated is another matter), and will always roll d20s to resolve things. Just as there will always be mages and clerics, the ranger has become somewhat of an integral part in all that is D&D, and as such it should always be defined as a class even if it makes more sense for it to be something else.
Finally, many have mentioned that they would like "DnD Next" to contain only the four base classes - fighter, thief, mage and cleric - and create all other types of classes using themes, backgrounds, etc. The problem with this is that it really overcomplicates the class design; all of a sudden, you have a "fighter" that can be defined twenty different ways, and each one of those ways has to be explicitly worded so as not to cause confusion with each other. By separating like minded themes in to a new class, it makes the creation of both classes significantly easier. I won't have to wade through five different ranger-like themes when I want to create a straight up fighter.
So, please, let's keep rangers as their own class. Besides, it'll probably be the only way I'll once again get my velociraptor animal companion! 
