Too much and some things could be easily skipped :

- Amsterdam 3 nights

- Berlin 3 nights

- Prague 2 nights

- night train to Budapest (1 night)

- Budapest 2 nights

- Vienna 2 nights incl. day trip to Bratislava

- night train to Zurich (1 night)

- Switzerland 3-4 nights

- Paris 3 nights

Swiss cities aren't that nice, if you visit Switzerland go to the Alps at least

You need to book Eurostar (30€ seat reservation) well in advance btw, there is a limited quota which can sell out weeks in advance

We find that a pattern of 
Day 1 travel from A to B

Day 2 (or more) in city

Day 3 travel from B to C

Otherwise you get up, breakfast, grab a train for several hours, arrive mid - late afternoon, find accom, quick tour and evening meal, bed, get up………..

So 1 travel - 2 nights - 1 travel - 2 nights…….

As above, I would advise consolidating a couple of the legs rather than spending ~10 of your days traveling between places and having only ~10 days in the cities themselves.  Even though the trains might only be a few hours, unless your choice of accommodation is optimal then you will find you spend a bit of time on either end getting to and from wherever you are staying.

There’s nowhere on your list that I would specifically cut out - except Switzerland if you are trying to keep to a budget.

We were in Hamburg recently and made a day trip to Bremen - it had been on our list but we couldn’t manage to get a timing that worked with overnights in both cities.  Instead we stayed in Hamburg for a couple of nights and got the train to and from Bremen in a day.  It was enough to give us a feel for the city and to put it on our “will visit again” list.

Hi there

I would suggest more than one day in Budapest, when we visited before we stayed 3 days. This time we are only there for about 24 hours. When you go to Switzerland, it can be a very expensive country, so we tend to go there and leave as soon as we can. We take snacks and food with us to cut down costs. 

Your Interrail pass is valid on the Bernina Express and the Glacier Express, these are panoramic trains that go through the alps across Switzerland, so you could do something like that instead of the cities. You do have to pay a reservation fee to use the train but it was about £25 each. 

Interlaken is a great place to visit on an interrail trip and you can use your pass on a boat trip there too. 

There isn’t two days of stuff to do in Belgium and Antwerp is a much nicer place. If you are travelling between Belgium and Amsterdam, try to avoid the Belgium trains. They might be free from reservations but they are rickety and uncomfortable. I do this trip quite a lot between Antwerp or Brussels and The Netherlands. Try to use a Dutch train if you can. 

Lastly try overnight travel so you wake up in the different cities. 

Avoid the Glacier and Bernina Express : 49 and 19 CHF seat reservation. It's full weeks in advance and very crowded

Instead take reservation-free hourly regional trains on the same route : pull-down windows, less busy, more trains

You can sit on the first reservation-free coaches of the Bernina Express too

There are multiple nice cities in Belgium: Gent, Leuven, ...

A general comment like this is bound not to be correct in many cases. It very much depends on which train you use.

For travel to Amsterdam, the hourly intercity is always recommended.

I had to book mine a few weeks ago for mid August, one of the trains was already fully booked for first class. I paid 26CF for each person in first class. But as I am travelling with a 13 year old, I wanted her to experience the panoramic carriage :)