^^^ I read that series long long ago... At the time I didn't even know it was going to be about gay....
As for writing a new story... Understand that all the stories that ever can be have already been written. Chaucer or Shakespeare did them all.
http://www.ipl.org/div/farq/plotFARQ.html explains it all.
So any story you write is going to be like _______________ - Sure, different named character on a different world/at a different time - the background setting will be different, the dialog in a different language, but its all going to be the 'same' as a story already written.
The masters of fiction pull it off because they can paint new interesting characters, or put in interesting details in their world. They have witty or surprising dialog that strings the reader on. But the story, the basic plot has been done - redone.
All stories boil down to resolving a conflict. Maybe not a war, but something, some conflicting thing - is going on and our protagonist needs to find resolution. How s/he does that, and what venture you take us on to get it done may be interesting, if you can keep from falling into obvious strings... That is a hard one.... you can get a reader interested in a story where no one gets killed, no one gets terrified, no one is thrilled.
I read the Amber Series long ago, I found the whole concept to be nice. So yeah, I can see it done with gay characters... But if you make it overl gay you will be greatly diminishing your reader audience.
Mercedes Lackey (As Mr. Tinklers pointed out) didn't let on that this was a gay story until after you bout the book or started reading it. And the first book of the series was so well done and the story so 'good' most people who wouldn't read a 'gay novel' completed it and reached for the next in the series.
The 'gay' was there, but it wasn't everywhere, and it definitely wasn't the main thrust of the story. The main thrust of the story was about Magic and of course the conflict, and the story just happened to a guy who was gay.
Now if you can pull that off, kudos to you. Unfortunately too many people start off wanting to write a gay story and that is exactly what they got. So instead of looking at your story as must having gay characters, try working on it with straight characters to flesh out the real story and let the fact that characters are gay be more of an 'oh by the way.....' instead of the main feature.