I think Ancelotti summed it up well. The way I saw the match, we played 4-4-2 / 4-4-1-1 in defense, and in attack we played 4-3-3. The problem in attack was several:
1) Holgate and Mina were unable to take advantage of the numerical superiority. There were too many horizontal passes, and they did not challenge the opponent's line.
2) Davies must stop running after the ball when Holgate and Mina have the ball. He attracts opponents, and ruins the room for Mina and Holgate.
3) Gilfy, AD and DCL were all too often positioned on the same horizontal line. It is easy to defend against.
4) Richarlison and Bernard all too rarely attacked behind the defensive line of West Ham, instead they sought to position themselves in the central corridors.
5) Points 4 and 5, lead to us getting little width and depth in the game. It will be especially difficult to play between the lines. As West Ham's lines can have very short distances inside and between them.
6) We need to switch fields much more often, and then seek out the space between the lines.
7) We lose too many 1 vs 1 duels. In the future we need players with good 1 vs. 1 skills.
8) Neither BG, Sigurdsson nor Coleman are good at crossing the ball. Then we also lose DCL's greatest strength.