Do you have similarly impossible expectations for hotels and restaurants, too? If four stars is mediocre...
For restaurants I always check Yelp and don't go to any under 4 stars with min 100 reviews. The few times I've broken this rule in the past (due to being too hungry) I always regretted it. For hotel I compare a bunhc of average review scores (booking, expedia etc) and don't go if under 85%.