I have had a look at Steam250's list of hidden gems released this year. I have tailored the list to games in the 14.99€-20€ price range with 100 to 600 reviews.
I might as well list the results below for everyone else to enjoy.
~ 500 reviews, 97% positive
~ 400 reviews, 97% positive
~ 300 reviews, 99% positive
~ 200 reviews, 98% positive
Edit: You can easily browser similar results on GameDataCrunch with a filtered view:
Top hidden gems on Steam, sorted by hidden gem score
www.gamedatacrunch.com
Here are 4 other hidden gems release this year found using GameDataCrunch.
~ 300 reviews, 97% positive
~ 200 reviews, 96% positive
~ 200 reviews, 95% positive
~ 200 reviews, 95% positive