Pathfinder has come so very close to giving me what I want. Shapeshifting is my favorite thing to do, but few options allow me a taste at level one. The two options that come to mind that come the closest are the Feral Hunter and the Metamorph Alchemist, but neither are quite it.
The feral hunter gets an infinite use of a polymorph ability with an animal theme, but this ability only provides a flat buff. No natural attacks here. And it's not much of a polymorph, oddly colored eyes and furry skin as the text proposes leaves me wanting for something better.
The Metamorph gets alter self at an hour per level from level one. This is neat, some humanoids get natural attacks, and some get neat abilities, swim and scent coming to mind. And a buff on top of that. But it's an hour per level and it's alter self until level five, and to be honest, I'd rather be animals.
To be honest, my dream would be an official conversion of the shapeshift druid variant from 3.5e dungeons and dragons. But it doesn't fit perfectly, there's holes in the rules (stuff like senses, disguise checks), and the buffs given are way too much when compared to the way wild shape already works.
So with all this in mind, here's my attempt at something close to what I'd want. The following is a druid archetype.
At level one, the druid does not gain a normal nature's bond, but does gain a formshifting ability. There is no limit on times per day or length of time, and functions in some ways as beast shape I when it comes to animal forms available. However, ability score changes function as if using Alter self, and special abilities, movement speeds, and senses function similarly (thus preventing the druid from getting a level one fly speed).
Now, one idea I have is that similarly to the animal shamans, there is a delay in wild shaping. And by that, I mean that the ability doesn't behave like beast shape I until level 6, and other improvements are pushed forward a similar amount. Like the feral hunter, the druid does not get access to elemental or plant forms.
Alternatively, I could simply write it in a way that prevents the druid from taking wildshaping feats, meaning that they do not get to spell cast in animal form, enhance their transformations, or speak while transformed.
Or I could do both. I'm not sure exactly how to balance it perfectly. Some arguments I have for my choices being fair are as follows.
Scent at level one can already be gained by half-orcs and orcs with a feat, and that version wouldn't be cancelled out by an antimagic field. The bonuses gained by alter self would be the same gained by feral focuses used by the feral hunter (and the hunter can get a bonus to con as well, where the druid would only get dex or str). Not to mention that the hunter can still use armor and weapons as normal and still speak while using their own ability. The swim speed is a little bit unfair, several animals get a swim speed, such as an octopus, monitor lizard, and dire rat of all things. A few races get this standard though. And swimming doesn't come up much in the campaigns I've been in. And there are plenty of actual weapons that work better than natural ones.
If anyone has any feedback on how I can improve on this archetype, I'd like to hear it.
Personally, I think the concept works better as an entire class rather than an archetype. I actually published my thoughts on the topic in Rogue Genius Games/Everyman Gaming's product, Paranormal Adventures.
The problem is that turning into animals is not a 1st level ability (despite the existance of a couple of obscure ways to accomplish). So there would need to be a compromise until you reach the appropriate level. Several game options try to accomplish this by letting you become like a humanoid animal, like with skinwalkers and the feralhunter hunter archetype.
I agree with Alexander that the concept of a shapeshifter is broad and interesting enough to warrant an entire class. Heck, I even have one baking in my design oven. However, I don't think homebrewing a whole class is a good idea. Classes are really big projects that need a lot of content and work to tweak and balance.