Systm0fD0wn

A few friends and I are thinking about traveling to Europe in May/June of '09 for 2 to 3 weeks. We'll probably be getting the Eurail Global Pass... or maybe a flexipass. Anyways... I have been looking at the route we could possibly go to visit a decent amount of place in Europe during this time. Seeing as though Eurail doesn't cover England, we were thinking about flying into London first, and then flying from there to either Naples or Rome (depending on the price and the slots available) because my friends aunt lives in Naples. So here is a list of cities from first to last that we could possibly visit.

London (fly to from Boston)
Naples (fly to from London, then Eurail from then on)
Rome
Florence
Pisa
Milan
Paris (overnight train from Florence, Pisa, or Milan)
Lille
Brussels
Antwerp
Amsterdam
Arnhem
Düsseldorf
Cologne
Bonn
Heidelberg
Stuttgart
Munich
Salzburg
Vienna
Venice (overnight train from Vienna)

I realize that this is probably far too many cities for three weeks, but it's just a list of places that fit the route that we'd be going on the trains. Most of the cities are within 2-3 hours from eachother. I'm wondering if any of the cities listed are not worth it, or if any additional cities are a must that are within the route we are taking. Also... cities in bold are cities that are kind of a must for us to visit. Any input/advice would be greatly appreciated.