Here's the answer to your question, Dida: it's highly regarded because it lets you make grand, sweeping generalisations about anything you feel like.
It's understandable to not like 2001, even within the context of other science fiction.
At the same time folks like contre are right that almost the entirety of criticism you hear is just people being people who don't appreciate cinema techniques and its history and would probably find any old movies boring. If you want to dismiss any sort of "classic" work as boring and terrible in the modern day then you at least know what you're doing, and 2001 is then not unique at all compared to any old movie you could choose to complain about. I think you could say objectively that 2001 still holds up far better than many others - something like Gone with the Wind is awful racist trash by modern sensibilities though is viewed as a "classic." As for the first part, disliking the various science fiction elements presented in the movie, there are acceptable other opinions:
Solaris is a better film because it's the only visionary movie unfettered by corrupt capitalist influences.
You prefer some other abstract science fiction movie (typically Blade Runner) because you strongly prefer a specific subgenre (e.g. cyberpunk)
Any other opinion: You don't get sci fi.