Try changing your voice settings; you'll find them in the "Voice Settings" tab. Each attempt to generate a voice will bring a different result (especially visible at low stability). The performance of the voice is also highly dependent on the voice itself; if you are using a pre-made or voice-designed voice, it tends to be more tempered and less emotional, while a cloned voice tends to exhibit a wider emotional range but also highly dependent on the original voice used for the clone.