So, I guess I'm obligated to make fun of werewolves as well, as well as other changers, just for the sake of fairness. So...
The Psychological Were: In a surprise twist, the were is not able to actually change shape but instead regresses to an animal-like personality, becoming a lot more fearsome, capable of doing harm to others, and generally acting like an animal. This can work, but the writer makes the mistake of allowing some human mental processes into the mix; familiarity with someone is fine, but memorization of passcodes and advanced strategy is a definite issue. If the point is to make a statement on the human condition by showing that we are all animals, then it gets undone by allowing the animal access to his human abilities; all you have is a psychotic human who is using his animal urges as an excuse to commit evil, and that really does not make the point.
The Teenage Werewolf: There's an obvious analogy between puberty and lycanthropy; the sudden growth, the increased strength and body mass, the rampaging hormones. It has not been lost on horror writers. When it's used well, it works out great; note the difference between Teen Wolf and Teen Wolf 2. However, the problem is that werewolves are being used more and more as replacements for vampires, including the supernatural boost to angst. Although the angst is understandable, given the chances of accidentally killing someone while transformed, it still feels awkward; the point of being a werewolf is the temporary lack of restraints and to saddle them with all of the negative human emotions will always be weird. They just need to come to grips with who they are; a few counseling sessions would improve this character by leaps and bounds.
The Were of Vengeance: Okay, so I get this one: A guy finds out that he can turn into a werewolf and so decides to take advantage of his were form to kill people, possibly becoming more animal-like in human form. The idea here is to explore those little wishes of revenge that we all have and why they aren't necessarily good for us. The problem is that the writer goes overboard on the idea at some point, and makes the were virtually invincible, possibly to suggest the need for revenge can be overwhelming. The problem is that if you're going to show something as a problem, you also need to show it has a solution, be it forgiving your targets or getting killed because you have become worse than those you prosecute. The irony here is a variation on the psycho-were; you are using an animal to express higher mental functions, and once that happens your story invariably goes off-track. End it quickly, or transform the person into a defender of the weak; either way find a resolution before your readers want to put the were down.
The Out of Control Alpha: This is a relatively recent modification, but one worth noting. The alpha of the pack becomes so invincible that no one can do anything about him, and he rules his pack with an iron and ruthless fist. The pack either takes over some major crime ring or becomes a force for anarchy, and although some of the pack wants to do something about him they are too scared of him. This character is usually meant to show that either mankind is no better than animals, that leadership can corrupt, and/or absolute leadership is a bad thing. The obvious problem is that the writer forgets that he's dealing with humans; any solution to a threat works, and, unlike our animal brethren, we are not limited to hand-to-hand combat. Yeah, a basic hunting rifle will solve the problem just fine, or even, in extremis, a slingshot with a silver marble. You can argue that the pack won't respect someone who wins this way, but the winner does define the rules after all, and the usual rule is to honor the new alpha, and any threats from the old, DEAD alpha should evaporate with the wind as the new political structure solidifies. There will be chaos in the wake of his death, but that should work out well for any decent writer.
The Funny Were: Okay, this is cute, and can work out really, really well in the right hands. The concept is that you are taking a random animal, one that people do not usually associate with lycanthropy, exaggerate the traits, and then make a humorous statement on the human condition through satire. The catch is that it takes a really fine control to make it work, and someone with a very definite point in mind, or else it comes off as more silly than humorous, and the point may be lost. The key is to not make the point too broad, while at the same time applying it to humanity in general; a fine balance point, to be sure, but if you can find it your story will really work.
The New Were: Sometimes people get tired of the usual suspects, and so create a new kind of were. They either research a specific species or come up with one to fill a niche, and sometimes a little bit of both, but any case a new changer is born. The key in all cases is to make sure that your new were fills a niche, or you will get a lot of weird looks from readers; an animal that is just there and doesn't bother fitting just feels like a waste of space. My personal suggestion is to avoid the trickster and warrior roles, as they have lots filling those spots already. Another issue to bear in mind is to not mess with existing too much; if you find a were-antelope that already fills a specific niche for an African tribe, for example, don't mess with it too much or you may offend someone who actually knows about it, and then you have troll issues. Basically, fill a niche or keep it to an established niche, and you should do fine.