Yes there is a different feel between the trilogies and it's entirely deliberate. It's all about the story. The prequels take place in the heart of the Republic. It's crisp and clean but the aesthetics only serve to paper over the cracks. The Republic is dying, corrupted from within and the prequels are basically about the gradual decline of the Republic. The Senators and Jedi are at the heart of Republic affairs. It's only when we visit Tatooine that we realise for the first time that the Republic isn't as effective and functional as they would have you believe. But Coruscant is at the heart of the prequels. What happens there affects the rest of the galaxy. The Clone Wars take place all over the galaxy but it is a war shown through the eyes of the central figures in the Republic and Confederacy. The original trilogy is set in the fringes. It's a small group of rebels battling an Empire after 20 years of dictatorship. Coruscant is a distant memory. Everything is dirtier, grittier, there's no hiding the poisonous nature of the galaxy anymore. Compare the first worlds we see in The Phantom Menace and A New Hope. In Phantom Menace we see Naboo, a planet with great beauty, fields of green, cities made to be beautiful. It is the image of paradise, a paradise that is quickly overrun by the uniformity of the droid armies, a glimpse at things to come with the Empire. Now look at A New Hope. The first planet we see is Tatooine. A lonely, desolate place with no hope, no function in the wider galaxy. It's is backwater planet that nobody cares about or pays much attention to. There is no beauty here, only a struggle to scratch out a living. The different feel is completely intentional. They feel like different galaxies because in many ways they are different galaxies. The feel of the OT is a direct result of what happens in the PT.