It is quite possible that an individual does not feel either good or bad about a piece of artwork. Sometimes this may be due to the inability to discern the finer points. It is perfectly fine if at times you do not have any particular opinion about an artwork. Art appreciation requires that you do not force yourself to have an opinion. Such a forced opinion comes more out of the necessity to make an appreciation rather than ones genuine appreciation for the artwork. Forced or faked appreciations are not well taken and do no good. Be yourself and express your genuine opinion.