Amex still has lower acceptance in the Europe than say Visa or Mastercard, particularly in Germany where the debit card remains preferred over credit cards in many establishments. However in other countries the acceptance improves significantly, in Switzerland for example I have been able to use it in most establishments. I would say that ignoring Germany you should be able to use it 80-90% of the time, in Germany its far less probably max 50%. In general through hotels will accept the card, as will most restaurants but retailers may be more picky.

The only thing I would watch though is the FOREX conversion rate which is worse on Amex than on any of my other cards. While Europe is mainly in Euros some countries are still using their own currency e.g. the UK, Switzerland and Denmark etc.