If you like to see tourist stuff in the larger cities but don't want to spend much time I recommend taking bus tours(hop on hop off if possible) It will take you to all the main sights and drop you at the doorstep. Else it takes a long time to get from one place to the next, and if you make a mistake you may end up missing it all together.
Oh, if you're starting from Paris, go: Paris, Luxembourgh, Brussels, Amsterdam, Hamburgh, Kopenhagen, Oslo, Stockholm, Berlin, Prague, Vienna, Budapest, Vennice, Rome, Monaco, Barcelona.
This will skip Londen and Finland but they are a long way to travel, with not much to see that is not in other places.
Also, skip scandinavia if you want to save time. It is nice, but a bit out of the way.