There are also a few hidden backgrounds from the original Mortal Kombat. I would say that MK2's sound is up to par with the arcade version. All of the voices are included in this version. The sound samples are also recorded at a high sampling rate. On a fast 486 the frame rate on high detail should be around 30 fps.
Video cards seem to make a big difference.
Ram is also a factor. With the graphics on high the backgrounds are exactly like the arcade with everything intact. When the graphics are set down some of the detail of the backgrounds are dropped for speed purposes. After playing all of the different version I think that the PC version is the best arcade translation. The PC's graphics are far more crisper and lifelike than the console versions.