Need my 4 week Europe itinerary vetted, please

This is my first time going to Europe and / or doing multiple countries in a single trip. Might be gruelling, might be fun. Just the first plan I could think of. Looking for feedback!

Day 1: Land in Paris, settle in, see around.
Day 2: Explore Paris more.
Day 3: Half day at Paris, take train to Bordeaux, settle in, explore.
Day 4: Explore Bordeaux more.
Day 5: Half day at Bordeaux, fly / take train to Brussels.
Day 6: Explore Brussels.
Day 7: Half day at Brussels, fly / take train to Amsterdam.
Day 8: Explore Amsterdam.
Day 9: More Amsterdam.
Day 10: Fly / take train to Dussledorf, settle in.
Day 11: Explore Dussledorf.
Day 12: Half day at Dussledorf, fly / take train to Berlin, settle in.
Day 13: Explore Berlin.
Day 14: More Berlin.
Day 15: Half day at Berlin, fly to Rome, settle in.
Day 16: Explore Rome.
Day 17: More Rome.
Day 18: Half day at Rome, take train to Milan.
Day 19: Explore Milan.
Day 20: Half day at Milan, fly to Barcelona.
Day 21: Explore Barcelona.
Day 22: More Barcelona.
Day 23: Half day at Barcelona, fly / take train to Madrid or Seville.
Day 24 & 25: Exploring Madrid or Seville.
Day 26: Depart.