Colours and sounds seem more vivid. Everything appears to flow. LSD causes perceptual distortions or hallucinations - while someone is tripping they can affect how they perceive their environment. The environment will also dramatically affect how the tripper feels. Change the environment and the nature of the trip will change.
Time becomes meaningless.
It is impossible to tell whether a moment has lasted a moment or a million years. Senses can become confused - you might taste colours or see sounds. It's common for people at the peak of a trip to experience a sense of depersonalisation. They don't feel like an 'I' anymore. They experience themselves as just a part of everything else.