An opinion is a view or judgement formed about something that doesn't have to be based on fact or knowledge. It is a completely subjective statement (based on or influenced by personal feelings, tastes, or opinions). It reflects the speaker's personal views and thoughts.
An observation is the process or action of observing something or someone carefull in order to gain information. It is generally an objective comment (not influenced by personal feelings or opinions in considering and representing facts); the person making it does not wish to express a personal opinion on the subject but merely makes an observation regarding it.