Eh, I don't think Spielberg is that great of an action director. That said, he's a great director.
What Spielberg has (and Cameron too) is the ability to tie action to the narrative in a way that makes what you're seeing on the screen carry some kind of emotional weight and further the story along. I think a lot of directors simply come from a microscopic school of thought, and go out to film the most elaborate, frantic action scenes possible, without once thinking about how those shots can further the story along. We're an MTV generation; we want YouTube clips, not slow, meticulous set pieces setup by long stretches of tension.
I mean, I know younger people that think the chase sequence in the first half of Terminator 2 is boring. That's right, boring.
Perfect example of this is The Matrix. The original is incredible, and the Wachowski's don't waste a single action sequence that doesn't connect to or move the story along. The subway duel is fantastic because it marks a significant turning point in Neo's character arc, combining both well-choreographed action and a compelling story. The sequels blow - hard - because all they are is a series of disconnected action sequences.
I find the primary factor behind of all this is just what Solo said, that a lot of younger directors cut their teeth with music videos and try to bring those sensibilities to feature-length productions. The other factor is the short attention span of mainstream audiences.
We might think long, character-focused action sequences built up with long stretches of tension to be awesome (and it is), but I don't think we (as in myself, Ichirou, Solo, etc.) represent the mainstream at large.
