Too many destinations in too short a time. You're going to be utterly exhausted from constantly being on the go, spending more time in trains than actually seeing destinations.
My advice: Cut the amount of destination in half. It'll still be a full itinerary then (fuller than I'd personally like - I vastly prefer to linger and get to know places a bit), but at least you'll retain memories to distinguish those places from each other.
yes... your are right... and which cities would you cut?
Wow, you've planned to move a lot!
Give yourself at least a couple days in each place, and don't forget that you will lose a lot of time on your travel days - not just travelling, you'll have check ins and check outs, finding your way to / from the station and orientating yourself. Are you dead set on your start / end locations or do you have some flexibility on these as well? What are you looking to accomplish / are there any places that you deem priorities at the moment? Have you allowed for day trips from central locations anywhere instead of moving directly from place to place? For example, when I was in Belgium I spent 8 days in Antwerp, but did day trips out to Brugges, and Brussels while I was there so I didn't have to carry my pack and actually felt more settled.
If you want to do a north to south or a loop, pick a shorter distance to cover with longer stops and you'll likely enjoy yourself more and won't feel like you spent all your time on trains and in and out of stations.
If you can give us a bit more information on what you're interested in we might be able to give you a bit more direction.