I am learning Hungarian Rhapsody No. 2 and am able to play all of the cadenza-like parts at a respectable pace, but I can’t seem to achieve that "glissando" feel that all of the recordings have. Do I just need to keep practicing, or is there some special technique professionals use to play fast scales?
There was a famous quick-draw pistolero who used to say "Smoothness is nine tenths of speed."
That’s true in music performance too. Practice very very very slowly with a metronome.
Those last three words are the important parts of that paragraph.
Practice at eighth=70 through the fast parts. Concentrate on NAILING every note securely and connect it beautifully to the next note.
Only increase the tempo by one or two bpm but not until you can solidly strike every note and make it sing.
Take all the slop out of the notes and the transitions between notes.
Slowly increase the tempo. What do you hear? Aha! It’s magically better, isn’t it?
The key to speed is slow, smooth practice. With a metronome.