I don't consider "good for its time" argument valid, but even with that in mind, this movie is a bad one. Whoever wrote the script does not understand how math, science and universe in general fundamentally work which results in cringy moments. There are always assumptions in SciFi, but you have to make them consistent with reality or you should have explicitly made it clear that movie universe is purely fictional. I don't recommend watching this film if you graduated equivalent of European high school some time after Enlightenment. And of course it is super long and boring, with constant multiple shots of the same thing, which are overly long by themselves and often are not needed for the plot.

The last 30 minutes are really good and interesting. But getting there is slow and tedious, i almost fell asleep. [spoiler] plus they never explain why the aliens abducted all those people and why they suddenly decided to let them come back [/spoiler]

So we sit through 2 hours of mostly boring scenes linked together with bad transitions and don't even find out why the aliens came in the first place? Why they abducted those people and why they suddenly decided to return them? What in the HELL were they even saying to each other when the people and the aliens were "communicating" through those beep-boops and lights? Why didn't anyone question it? What was so special about that mountain? Why did that guy go off with them in the end and how come they nodded and smiled to him instead of being worried or something? Everything was so random and boring. This is possibly Spielberg's worst film.

When people say this movie is boring is because when they hear alien encounter, they expect something like Independence Day.

This movie is so bad in so many ways. Its meaningless, boring, etc. 2 hours time wasting. It is plain and simple shit.