In the world of cinema we have what we call "movie cycles" which, in a way, you could call "copies" of other works. Akira Kurosawa was very much influenced by Hollywood westerns and when he created Seven Samurai, and it was very successful, America borrowed the base line of the story to recreate it into Magnificent Seven... since then the movie has been remade over and over, shifting with the demands of the public and the style of its time, but key scenes and basic story lines are still there. 2 other movies that were spun off the same original one were The Three Amigos and A Bugs Life. We're due for another remake in 10 years or so.
With that in mind, even as an anime fan myself, I can't say "rip-off" to anything that's recreated. just because it uses some similar ideas, doesn't mean that the film is not original and can stand its own ground.
As for Inception and Paprika it is very true that they are extremely similar, but I wouldn't say it was "based" on inception... maybe borrowed ideas, but other than that it is an original work in and of itself. I recommend you watch it!