There are 128 presets in ROM, divided in bank A and B.  These cover the pop/rock territory pretty well, with a few surprises (ethnic and special fx).

The MT-32 can be considered the "uncle" of General MIDI (GM), in particular of Roland's famous Sound Canvas SC-55, because it paved the way for that standard.  Many of the sound categories found in the MT-32 are followed closely by the GM standard.

Interesting to note is that not all the editing features are controllable from the front panel, but they are accessible from a sequencer or computer editor.  The front panel only allows simple adjustments such as changing part volume, tuning, reverb mode, and MIDI channel.
 

Note:  the first thing to do upon turning on the MT-32 is to press "MASTER VOLUME" and the "5" part button at the same time, press the "1" part button.  This will reset the MIDI channels one through eight, and when playing - typically - from a MIDI keyboard set to channel 1, it will play.  If you don't do this, you're not going to be able to hear anything because for some odd reason the MT-32 factory MIDI configuration sets part one to MIDI channel 2.  Channel 1 has mysteriously disappeared.