As with anything else, some are better than others. Of course, the difference is that in professional work, you have to sell your story or your pitch to an editor, a producer, etc. and outcompete others vying for the same slot, so there's a selection process that (in theory) weeds out the weaker entries; whereas in self-published or fan work, there's no such selection, so the ratio of bad stuff is likely to be higher. But there's still some stuff that rises from the pack, and some fan authors/filmmakers manage to graduate to pro work.
I admit, though, I've never understood people who will go to great lengths and expense to lovingly recreate an old TV show with professional skill, yet have no interest in creating anything original of their own. Heck, when I first started making up stories in the Trek universe as a kid, it was something like 6 months before I decided that conforming to Trek's ideas was too limiting and started creating my own original universe instead. Original fiction is much more liberating -- plus you can actually sell it for profit without getting sued by its owners. So I don't get why the people who complain about not being allowed to make elaborate 2-hour fan films because of the strict guidelines don't just write something original and shoot that instead.
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