Park Güell

I give Park Güell only 3 stars not because it looks boring but because it's just an average attraction amongst all attractions in Barcelona.

Actually, this park is better-looking than most of the parks in Europe. But when compared with those of Sagrada Familia, Casa Batllo, Palau Güell, and La Pedrera, namely those uniquely designed buildings in Barcelona, the architectural design of Park Güell doesn't look that amazing. If you travel to Barcelona for the first time and can only spend one day in Barcelona, I won't suggest you waste time on Park Güell but will recommend the above-mentioned four attractions. 

Additionally, the monumental zone is so small that it's not worth the admission fee. Park Güell is divided into two parts, the monumental zone and the woods. The woods is free of charge, but there's simply nothing to see in the woods - it's just like any green space in any ordinary park; to get into the monumental zone, where all the design by Antoni Gaudi is, you need to pay 8 euros (7 euros if you buy the ticket online). However, the monumental zone is small and fully exposed, so you can actually see all the things there from outside the monumental zone. Even if you get into the monumental zone, you'll finish your visit very within 20 minutes, because it's a small area. And big crowds of people will accelerate your visit. All in all, it's not worth the money. 

Anyway, as I said before, it's better-looking than most European parks. If you are a park enthusiast, then go visit Park Güell. In other parks, you can't see so many Antoni Gaudi elements.