Sure you can. The question is how much do you want to write a good one?Writing a fantasy novel isn't really something you can "want" to do.
Consider how many SF/Fantasy novels come in trilogies these days. In my opinion, the only ones that have been consistently good are the Dragonlance novels. Other series have done adequately well, and then there are those planned as a trilogy (or other multi-book numbered series) just because "that's what sells."
Too much writing these days has become focused on "what sells" -- not about "what's good."
For example, how many people here in OT have read any of the Kevin J. Anderson/Brian Herbert Dune novels? A member of my Dune forum has nicknamed them "Dumb Novels" because the quality of the stories is so terrible.
Now I can imagine some folks here thinking, "but Kevin J. Anderson is a prolific author -- he's written scads of Star Wars books, X-Files books, comic stuff, other series, and the new Dune stuff -- and they sell."
Well, I concede they sell. But to somebody who grew up on the kind of science fiction that assumed that the reader didn't need to have everything dumbed down (as in basic science), these books are an insult. There are so many things wrong with these books, from the bad to nonexistent science, the lack of consistency and continuity with the previous novels in the series (ie. those written by Frank Herbert), repetitive exposition (as though the reader were incapable of turning back a few pages to refresh his/her memory of any forgotten detail), and the overall juvenile "gosh-wow" poor quality of the writing in general.
So it happened that one day Kevin J. Anderson and Brian Herbert sat down and decided to write science fiction novels. They wrote quite a few, in a really short amount of time. But their books are a very far cry from the masterful SF literature that is characteristic of Frank Herbert's Dune novels. Frank Herbert took many years to write his series, and during that time he did an immense amount of research, and questioning in which direction he wanted to take his characters. He never assumed that any mistakes he made would be overlooked by the reader because the reader was basically stupid. He respected his readers.
So we have three people who decided to write SF novels. Frank Herbert wrote his well. Kevin J. Anderson/Brian Herbert did not. It behooves every author to realize and accept his/her own strengths and weaknesses and not try to pretend to what he/she is not.
Erik Mesoy, it is possible that you really can say you want to write a fantasy novel. But can you write a good one? It's worth the effort to find out, so don't give up. It might simply be that you haven't found the right ideas to grab your imagination yet. And that part is crucial -- the story has to make you, the author, wonder "what's going to happen next." Because if you don't care, why should the reader care?

Or maybe fantasy itself isn't your forte. Maybe it's science fiction. Maybe it's horror, crime, or some combination-genre such as historical fantasy. As you continue to write and practice your craft, you'll eventually find the story that grabs your imagination and demands to be written.
