I consider CE3K (as it is known in some circles) to be one of the few classic sci-fi films of my own generation. There are so many good things to say about it. First, the story is introduced with an interweaving of mini-scenes that are designed primarily to feed a sense of anticipation that something amazing is happening. This is done very skillfully and its novelty at the time is less appreciated today because it has been borrowed so much since. As I recall, it was the first time I saw the use of the subtitled time and place data at the start of each scene as a dramatic mechanism. The acting is quite good, especially the interactions among Roy Neary's family members. What is striking about that thread is its depiction of a dysfunctional American family on the brink of divorce that seems so on target that it's as if Spielberg is channeling his own childhood (his own parents divorced when he was young). You rarely see that type of honesty in a major film production, but I do believe it was more common in the 60's and 70's. There is a lot of great cinematography, both in the landscapes and the glowing space ships that are placed upon them. The special effects still hold up today. And it had a great musical score as well that accented the other-worldly feel throughout. The orchestrated main title really illustrates this. And thanks to the time period, there was also a great disco version floating around, much better than the Meco track. It was hard to find but I located it here on youtube.
abduction scene of the little boy taken in the night from a little country house in the middle of a wide open farmland, or Dillon and Dreyfuss crazily trying to scale a mountain as military helicopters search them out overhead and dusk sets in.