I'm a huge fan of spy fiction and history, so you can imagine what authors are sitting on my book shelf. The best quote I've seen describing a novel was for Tom Clancy's The Cardinal of the Kremlin: If I were to write a novel with Tom Clancy level of detail when describing the job, believable characters and plots that would take 3-4 books to complete, can I called it a spy epic or spy opera? I guess you would have to look at what elements make a work of fiction an opera or epic and decided if those elements exist in the novel.
you can describe it however you like in marketting terms - i wouldn't use either in a query though. Epic is one of those bullshit words that means what you want it to mean - although its usually taken to mean that its long and convoluted - Opera (as in spy opera, space opera etc) derives from soap opera and implies that the facts are likely to be a bit wooly and subordinate to the plot.
Personally, and using movies as the example media, I would consider Ice Station Zebra and Red October to be more spy epic. Whereas any James Bond movie or Man from UNCLE would be spy opera.
Except when it comes to actual epics like Beowulf or The Iliad. Then they have a very specific criteria that your spy novel very likely doesn't meet.
Agree. It's one of those earned words, similar to "masterpiece." Later after it's been published, critics and the like will decide if it's an epic or not. Similar to Beowulf like @The Dapper Hooligan said.
I'm a proponent of inventing subgenres when a book doesn't fit in a particular one already. In a book store of course it would go on a different shelf -- I think B&N just puts Clancy under Fiction. Amazon probably has a category for spy fiction for example. I like the term Technothriller for much of Clancy's work, because it gets into the technical details of all sorts of professions. Spycraft, soldiering, politics, submarining, etc. To me, "spy epic" would generally be a contradiction in terms, since a spy is supposed to be covert, and epic implies grand, societal scale. I can't really think of any works that would fit into either genre. Maybe the collective body of James Bond films based on their length and societal importance.