european reeds are much simpler, and brighter, while more vibrant. they require more work on the part of the player as they are less stable. its more of a long scrape across. they are usually very light to play on, but again, requires more work on the part of the player's embouchure and air to make a darker sound and play in tune.
a good american reed is much more complex, and I guess a little harder to make, idk. It consists of the back, heart, and tip, with the spine in the middle, and thicker on the edges of the heart and back. They are darker sounding reeds and are sometimes a little less vibrant, so it takes more air from the player to vibrate the reed, but if the player is using good air, and its a good reed, it will most likely be in tune with a decent sound. they are much more stable in intonation and require a lot less work to play well in terms of embouchure, but require lots of air.