Online review sites such as Booking.com or Tripadvisor are considered to be the most accessible and valuable feedback platform in the hospitality industry (Verma et al., 2012; Xiang & Gretzel, 2010; Yoo & Gretzel, 2008). To keep pace with customers’ use of social media, hotels have recently begun to use customer-generated content or online reviews to assist in decision-making (Chan & Guillet, 2011; Leung et al., 2013) since reviews can affect customer satisfaction and ultimately hotel sales and profitability (e.g. Ye et al., 2011; Zhang et al., 2011; Kim et al., 2016; Berezina et al., 2016;). However, limited research efforts have been made to understand customers’ satisfactory and unsatisfactory experiences by analysis of online reviews (Kim et al., 2016; Berezina et al., 2016; Rhee & Yang 2015 a;b; Levy et al., 2013; Li et al., 2013; Kim et al., 2015; 2016; Kwok & Xie, 2016). Furthermore, the effect of different service characteristics on hotel performance is expected to be assymetrical and non-linear (Mikulic & Prebežac, 2008; Füller et al. 2006; Kim et al., 2016; Zhang and Cole, 2016). The objective of this study is to analyse online reviews and determine whether different hotel service characteristics have assymetrical or symmetrical effects on hotel customer satisfaction. A total of 8.540 online customer reviews (from Booking.com) for 42 4 and 5 star hotels in Athens, Greece were analysed in terms of the overall score of the hotel and the individual service characteristics (cleanliness; location/access; personnel quality; installation quality; room quality; food quality; service process quality, and perceived value) for a 2-year period. Data was analyzed using penalty-reward analysis (Mikulic & Prebežac, 2008) and the three factor (satisfiers, dissatisfiers, hybrid) theory of customer satisfaction (Matzler & Sauerwein, 2002; Matzler et al., 2003). Results show that there are indeed asymmetric effects on customer satisfaction. The most powerful frustrators are cleanliness and perceived value and the highest impact dissatisfier is room quality, followed by installation quality and food quality. Only personnel quality and location/access are hybrid factors, meaning that they can have symmetric effects on customer satisfaction. Also, no characteristic was found to be a satisfier or delighter showing that delighting customers is very difficult. Results also differ according to reason for travel (leisure / business) and type of traveller (solo, groups, families, friends). The results of this study can serve as a guide for customizing hotel services for each type of customer. This can lead to higher customer satisfaction and higher perceived overall performance of hotels as expressed in online reviews. Also, higher review ratings can influence overall profits.