Often it's read too fast. Reading a speech well is more difficult than speaking extemporaneously. There is little or no feedback so that you can't make subtle adjustments. Memorizing Memorizing your speech is even worse than reading it. All the objections that apply to the read speech also apply to the memorized speech.
Spontaneity is gone.
Often times delivery is too rapid. Concentration is on the words, not the ideas. Sometimes it sounds too formal, like a written essay. There is little or no feedback or other contact with the audience. This is analogous to the novice musician who has to stop and repeat when making a mistake while practicing.