My favourite pet peeves have already been mentioned - grammar, spelling (especially of names - sorry, but it's called *fan*fiction, and a fan should get the names of characters right IMO), PWP, OOC, overusage of OCs, Mary Sues etc.
As for pairings... hm... I prefer gen-fiction and the portrayal of friendship to any romantic story. Because, honestly, we don't get to see much romance on the show, but the interteam relationships are much more worth exploring than conjuring up some romance. If the plot's intriguing enough then I also read het or slash (Morgan/Reid, Hotch/Prentiss) - but the plot has to be the focus, and the romance slowly developed and staying within the PG-13 or at most R-boundaries as I don't need to read everything spelled out...
As for OOCness: I don't like Reid being portrayed as a damsel in distress. However, it would also be quite out of character for him to suddenly be able to physically overpower opponents twice his size and weight. It's quite a fine line with him. I really like the fact that despite his strength of mind he's also vulnerable and emotional, so turning him into a tough guy for no apparent reason would be a major put-off for me.
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As for pairings... hm... I prefer gen-fiction and the portrayal of friendship to any romantic story. Because, honestly, we don't get to see much romance on the show, but the interteam relationships are much more worth exploring than conjuring up some romance. If the plot's intriguing enough then I also read het or slash (Morgan/Reid, Hotch/Prentiss) - but the plot has to be the focus, and the romance slowly developed and staying within the PG-13 or at most R-boundaries as I don't need to read everything spelled out...
As for OOCness: I don't like Reid being portrayed as a damsel in distress. However, it would also be quite out of character for him to suddenly be able to physically overpower opponents twice his size and weight. It's quite a fine line with him. I really like the fact that despite his strength of mind he's also vulnerable and emotional, so turning him into a tough guy for no apparent reason would be a major put-off for me.