When Star Wars debuted in 1977, fans were intrigued by George Lucas' innovations in the science-fiction genre. Before that point, every sci-fi movie was polished to a shine, a clean futuristic world that just felt fake. Star Wars was dirty, it wasn't refined, but it was a lived-in environment. It was one of the first times that science-fiction felt recognizable.
Part of creating this used universe was employing practical effects in the film making, the use of puppetry and matte paintings, but that was the standard for the time. George Lucas was always leaning towards computer generated imagery, but it wasn't until the prequel trilogy that the technology for what he envisioned was even possible. That meant that when it came time for the prequels, every location in Coruscant or Naboo didn't feel real, and drained the emotion from the scenes more subtle than Darth Sidious' plans.
Furthermore, the original trilogy was marked by actors playing with their scripts. Harrison Ford famously told Lucas what lines he wouldn't say, and Star Wars is better for it, but actors did not do that on the prequels. Lucas was always a better storyteller than writer, and when the dialogue sounds as stilted and fake as the digital surroundings, we can only be happy that he sold the rights to Disney.