I've come to the conclusion than JRPG fans especially in the west will a JRPG positive review simply by virtue of being Japanese or because of fan-service. Fan-service to me are gimmicks but the difference is that they are based on pre-existing concepts.
So when you see a JRPG game with a 4 star score or higher on amazon I advise you to swing by the negative reviews. Often negative reviews are more in depth. Some negative review are the person's weird personal problem though so be careful. Be even more careful with Playstation store star ratings as Sony gamers (I am one as of recent) are more likely to give Japanese games good reviews. Almost every jrpg in the PlayStation has a 4 star rating or higher.
Fans Service Types(tentative):
Nostalgia from playing a older game in the series
Brand association with another game series ( especially Final fantasy)
Simply being Turn Based
Large damage numbers
Simply Having a Classes/Job system whther they are well designed or not
Over the Top anime character design
Simply being anime styled.
Scantily clad/over-sexy disproportionate anime girls/boys.