If it's a plain remake without any addition, new twists or own charm, no doubt, most of them suck and are redundant.
There are cases though, where remakes of the same material can be great.
Example: The Front Page http://en.wikipedia.org/wiki/The_Front_Page, orignally a Broadway comedy.
1st movie based on the Broadway stage play: http://en.wikipedia.org/wiki/The_Front_Page_(1931_film)
2nd movie/1st remake and one of my most favourite screwball comedies: http://en.wikipedia.org/wiki/His_Girl_Friday
3rd movie/2nd remake, one of many brilliant Billy Wilder movies and my favourite Lemmon/Matthau movie: http://en.wikipedia.org/wiki/The_Front_Page_(1974_film)
4th movie/3rd remake, not a bad one (the original material is just too good to be destroyed), but nevertheless by far the worst one imo: http://en.wikipedia.org/wiki/Switching_Channels
So in this case the 2nd and 3rd movie of the same material became classics.
There are other examples, where both, the original and the remake are great and became classic, e.g.
http://en.wikipedia.org/wiki/Seven_Samurai
http://en.wikipedia.org/wiki/The_Magnificent_Seven
http://en.wikipedia.org/wiki/Scarface_(1932_film) one of the defining movies of the gangster genre
http://en.wikipedia.org/wiki/Scarface_(1983_film) today better known than the original
