The movie is not about the twist. Stop thinking about the twist or Rosebud. It's just a tool to get things moving. Rosebud is not central to the life of Kane, it was just a part of it. Like the reporter at the end says "A piece of the puzzle".
See Kane's life as a whole, and not just the twist. The interesting part is how at the end of the movie, the viewer, the reporter, the people who were part of Kane's life and Charles Foster Kane himself, find out how little they actually knew about the him. Everyone has their own sort of view of who the man was. Every individual flashback, shines Kane in a different light, some view him as an egotistical man, a ladies man, a cynical, an idealist, a rotten bastard, a sell out a lost soul, etc.
The point of Citizen Kane is, you don't get to know who an individual is based on one act or a moment in his life, but the sum of all his acts and moments define and shape the individual. That's why Rosebud in the end is pointless. The reporter was looking for it's meaning cause he believed that was the key to unlock Charles Foster Kane, but in truth it wasn't. It was just another part of Kane's life. Rosebud didn't shape Kane. It was just his sled, a memory of a long lost life.
There are a lot of other things that make Citizen Kane good, and the greatest movie of all time. It was a movie that changed everything about cinema, since the camera work, the editing, narrative and story. It's not exactly an easy movie to fully understand, I recommend watching the movie with the commentary by Roger Ebert, it gives a whole different perspective on the movie. It also shows that there was a lot of silly stuff in it, like Pterodactyls flying in the background of one scene.(Really)
Edit: Orson Welles did better movies by the way. Touch of Evil, F for Fake and The Trial for instance. Though Citizen Kane was a groundbreaking movie and changed everything. The most recent example of a movie that changes the laws of cinema is There Will Be Blood by PT Anderson.(Which funny enough, is considered the Citizen Kane of the new generation)