This movie was amazing. Forget what you read from the critics.
Is the movie too long? No. Much like Avengers Endgame, it does not feel long
Is the movie not long enough to introduce 10 Eternals? No. When you watch the movie, you learn of the origin of the Eternals and why they have been hiding all this time, so there is no need for a lengthy origin story or history on each member
Is this movie different to other MCU films? Yes, but in a good way. It reveals more about the origin of the universe, our place in it, and suggests that the Eternals and Celestials are going to have an important role in the future of the MCU