There's a whole bunch of improvements, but a couple in particular stand out. Firstly, there's improved pitch control. Previously, pitch on the Model:Samples was in semitones only. More control is essential for getting your samples in tune with each other, especially if you're using stuff pulled from old vinyl. Secondly, there's now velocity as a modulation source, so you can use the force with which you hit the pads to control things other than volume. Harder hits could increase reverb level, for example. The update also brings a higher resolution LFO depth, which is a nice addition.

All of these features were on the Model:Cycles that was released recently –- an entry-level synth that costs just $299, so it makes sense its slightly more expensive older sibling would get them too. Model:Cycles has also had an update, but it focused only on minor bug fixes.