AXL is a really weird company. 

I don't mean that as an insult.  AXL produces VNs with very little variation in quality, consistently producing stories and characters that are fun to read about...  However, when I take a step back and really think about it, their characters are the same between products, right down to the voices and (to an extent) their appearance.

AXL is probably the only VN company out there that hasn't radically changed its visual style in the past ten years... in fact, it hasn't changed at all, save to get slightly sharper due to HD technology.  Where most companies abandoned old styles or melded them with new ones, AXL has remained the same, utilizing variations on the same character models, the same character personalities, and even the same music.

So why does each game they produce feel fresh and interesting? 

It is perhaps one of the weirdest experiences I've ever had with a company, but AXL manages to be interesting despite never changing.  Its games have decent stories, interesting settings (ex: The PMC-run military school in Mamorikata and the Search and Rescue school in Dolphin Divers, or its line of fantasy VNs), and generally enjoyable VNs.  Honestly, just because they never just do the 'go to a normal school and obtain a harem' style charage is a plus point in their favor.  I'd put up with a lot from them just for that, but the fact that they maintain a high level of quality in their narrative is perhaps the second-biggest point in their favor (the biggest one being their penchant for unusual settings). 

In the end, my last conclusion is the same as my first... AXL is a weird company.  It is interesting precisely because it doesn't go adventuring with anything but the setting.  Normally, I'd be the first to condemn a company for refusing change, but in this case, I have nothing but praise for them, since I hardly even notice that lack of change unless I take a second to look at it objectively.