The Hellequin series is really great if you like epic serial tales.  Each book contains at least one mystery, but they all tie in together in an overarching tale that is the culmination of thousands of years of events.  

The main character is Nathaniel Garret, and is a likable Private Investigator-type or contractor-type.  He starts off the series having lost much of his memory, which is really the first mystery and allows the tried and true literary device; fish-out-of-water to succeed.  You really become sympathetic to Nate and since he has lost his memory, he also doesn’t truly know what he is capable of.

This solves another problem in fantasy stories with powerful main characters.  The problem of being OP!  This guy starts off with some impressive skills, but much like Harry Dresden from the Dresden Files by Jim Butcher or John McClane from the Die Hard movie series, he still manages to get his butt kicked often.  Often you can see that he barely scrapes through, but you know he is going back later to take care of business!  

There is a subplot about his true identity and powers that runs through the series.  It involves curses that were put on him that are slowly (over centuries) fading away and allowing Nate access to more of his power.  So, he gets more and more powerful, but we are constantly reminded that no matter how good you are, there is always someone better, stronger, faster, etc.  

In order to survive, Nate has to rely on more than just his strength and power.  He uses a combination of technology, magic, friends, preparation, and luck to survive and thrive!  

The Avalon Trilogy is about characters you will come to love, and the Rebellion Trilogy is about a time when Nate loses all magic and has to figure out how to get it back and how to help people without his magic.  They all advance the overall story, so that is a good reason to read them!