OMG, it's glorious. George Reeves is second only to Christopher Reeve in the pantheon of the character's greatest portrayals, and it's a close second. He may not have Reeve's craft and subtlety as an actor, but he radiates natural presence, charisma, and charm. He's an active pleasure to watch every moment he's on screen, both as Clark and as Superman.
The first season is pretty much universally regarded as the series' best. It's often surprisingly dark and violent, frequently likened to a crime noir, and Reeves gives us a tough, rough-and-tumble Superman suited to the show's tone.
The color seasons (starting with season three) become much more whimsical and kid-friendly, and Reeves once again rises to the occasion, emphasizing a warmer, more avuncular Superman that fits the material and the target audience. While the black-and-white years are more suited to adult sensibilities, I still find the color seasons immensely enjoyable, largely thanks to Reeves and his able supporting cast. (Jack Larson, in particular, brings an entertaining comedic flair to his Jimmy Olsen.)
Mind you, you have to make adjustments for the time and circumstances these were made. The effects are obviously primitive, and the stories episodic and often formulaic. But it's a goddam classic, and George Reeves embodied Superman for a generation -- and for generations to come.