I'm not going to say Unown is good, but they were the first Pokemon with alternate forms (Unless you count Nidoran Male and Nidoran Female as different forms of Nidoran, but they were done in a way that makes them different species.) and the Ruins of Alph were a pretty memorable part of Gen 2. The different forms thing is less interresting now with more Pokemon getting forms and forms that do somehting though and the Ruins of Alph were last in a game... I'm not going to check how long ago it was...Unknown have a laxy design and look dumb. They only learn one move which increases how garbage they are.
Also, the third movie made Unown way cooler than they are in game... and way cooler than the rest of the anime... At least they had some time not being a borderline joke Pokemon.