Recently, the movie industry has been churning out "big screen" versions of classic "small screen" shows. The Brady Bunch, Scooby Doo, Charlie's Angels. This is a new trend, mostly because up until the last decade, there wasn't much good TV to be nostalgic about. Studios do this because of name recognition: "I liked the TV show, so I'm going to see the movie." Even if the movie is horrible, some fans will go see it anyway.
The trouble is that most adaptations rarely achieve the level of quality of the original. For example: Synthesizer trumpets. In the 80's you didn't get a brass sound from your keyboard, as much as you got a "blaht" with some sort of fixed pitch. As technology improved, now you've got digital samplers that when you hear it you say "Wow! That sounds just like a trumpet!" The problem is that's not much of a compliment. If you play the cheapest trumpet on the market, you get a sound that will sound like a trumpet. The adaptation is considered good if it just approaches any original (regardless of quality), while the originals are considered good if they really are good.
So too with movies. After leaving The Lord of the Rings, or Spider Man, I can't help but think "The original was better" or "Wow, that was as good as the original." But I don't think, "Wow, that's a great movie!" To me, the great movies are things that existed as movies first. They aren't merely trying to recreat the feeling of another project in a different medium. Indiana Jones, Terminator 2, the Matrix. These are movies first. And the comic book/TV adaptations of these movies are just poor imitations of them.