Admittedly the movie does have some very hard to comprehend plot devices, such as screeching music, psychedelic landscapes and giant space babies. However, the artistic value of these is part of what makes the movie what it is. It's certainly not a movie for everyone, but the precedent it set for the sci-if genre is clear. After watching the movie you can see the myriad of pop culture references that are made about the movie and where many cultural works draw their inspiration.
2001 is unique in the sci-fi realm in that it's physics are actually quite good. For example, the space station, and their spaceship, create artificial gravity by rotating. This may sound silly at first glance, but the rotation creates a centripetal force that allows the astronauts to walk along the outer shell of the craft with ease. This force grows stronger as you move towards the interior of the rotation, hence why they float as the move through the central tube and stand and walk on the floor that lines the wall of the craft. Certainly this is an example how the movie gets its physics right.
Overall I would give 2001: A Space Odyssey a 9/10. I loved the movie, but I think we can all agree the shear amount of off color vistas was painful to watch.