Erm, I'm not sure what the hell that was I just read. I've got mixed emotions on it right now.
Reflecting on only the X-23 parts...
One minute I'm scratching my head wondering how story elements apply like blood that's been to hell and back(X-23's ongoing went into the hell of her own mind, and not real hell, but it could be someone else's blood for that)*. Other spots seem to be okay though the written voice for this X-23 is hard to really get into with how angry it's being delivered. Some spots are awesome. Some spots are again rather headscratching like the genetic twin comment which looks like it was randomly changed from clone to genetic twin(clone is the soulless debate, genetic twin is a much heavier issue, but it can slide because of self-perceptions of the character and the anger her voice is carrying that may hinder pure rational thought on the issue). To be fair though, genetic twin is more accurate than clone per the previous minis and ongoing, and I am glad to see it used as opposed to continuing the derogatory clone remark that Dr. Rice perpetuated onto Laura that confuses many fans.
While I'm scratching my head one moment, they then throw curveballs that are awe inducing. (Symbiote hybrid X-23 clones, that's just pure win.) There are other spots that are fun and interesting too, but at times it feels like they are using references and sites for the information as opposed to having read the material itself that came before. At least that's how it feels for X-23. Her parts come across as information from quick conversations, wiki references, some reference sites, and some creative liberties. Some of it works really well, some it is head scratching inducing. All of it kind of screams not having the time to dive into the character themselves for a firmer grasp of the persona and history. There are some nice nods to X-Force via the cloned 'sisters', but then they diverge reflecting more of a "gotcha" moment than really adding to the previous elements of her stories. All things that could have been easily found on any fan blog, fan forum, or reference site though, and lack a feeling of depth to them as yet.
The ending anti-thesis baddies are interesting though. X-666 is pretty much the exact opposite you'd expect, but the one that really caught my attention as wow was Ichor(the anti-thesis to Venom**, which is also an anagram for choir and is a greek god reference). I'll admit it. I'm a sucker for designs like his. Out of the 4 shown, I hope Ichor remains and grows into something more in the Marvel universe.
So far, Circle of Four is promising, but I'll save final judgement for when all the puzzle pieces are out and put together. It's worth checking out, but be warned. It might leave you scratching your head inbetween moments of awesome.
*It is someone else's blood for the portal. The exact wording is "The blood of a mortal who has been to hell and back." X-23's blood is only a vial that was used for the X-23 symbiote hybrid bodyguards. This dissmisses any Valkyries or other Norse beings as well since they aren't 'mortals.' More than likely it's just the blood of the girl he shoves through the mirror moments before.
**Correction, later in the event it's revealed to have been the one for the Alejandra Ghost Rider.