At the time of this review, HO is 8 chapters into volume 3 (and there's a 3-chapter side-story as well). Obviously this is a long fanfiction and it's a very well thought out one. It's got a large cast, but also a memorable one, and strong plots.
Volume 1 covers the arrival of ALO, along with ~60,000 players, in Halkegina and the initial reactions, along with how they're sucked into Albion's civil war. There are a lot of plot threads going on here and no one really has everything their way. Of course, if you're really wanting to follow one plot then you may have to wait around.
Volume 2 covers longer-term consequences - and there are some doozies. Tristainian internal politics are on the boil, with help from Albion, but the Faerie have politics of their own as they have to figure out long term leadership. Meanwhile, characters like Guiche and Louise are doing some growing up and that's a painful thing indeed.
Melancholy Heart is a side-story, admitted by the author to be predictable in places, but sound nonetheless, covering the activities of a couple of older players who are finding a new lease of life in this new world.
Volume 3 is just getting underway, so it's hard to say where it's going but given Volume 2 left several plots unresolved it's going to be fun finding out.
If you've not read this yet, go read it. Or Yui will make puppy-dog eyes at you until you cave.