I visited the two north italian sites in 2014. Luckily, they are close together and can be combined easily.
Bergamo is a very beautiful city by itself. The old city sits on top of a hill, with the city walls all around, lots of medieval towers in the middle and the alps in the background. The defense ring is quite prominent, with an impressive entrance ramp. Still, most visitors will spent more time in the streets of the old city with its various churches, towers, shops and restaurants. I have no clue if the defense works here are significant from the military point of view, but they at least provide a splendid sight, both from the outside and as a viewing platform. I can highly recommend a visit to Bergamo as a whole, ticking off the WHS is just the icing on the cake.
Peschiere del Garda on the other hand is rather unremarkable. Most tourists come here for the access to Lake Garda. The fortifications are easily accessible and can be viewed while walking around the village core. Without any special interest in military history however, they will not capture the attention for very long. On the positive side, Peschiere del Garda is located conveniently on the train line between the WHS cities Verona, Brecia and Bergamo, and the old core can be reached by walking from the train station without a problem. I spent two hours here before proceeding, and had lots of time to spare.