Great design is much more than a creative structure that catches the beholders eye. First and foremost the design must follow three basic characteristics in this order: Function, Form and Color.
Function:
The design must have a sound purpose for all that inhabit the space(s). It is senseless to spend tens of thousands of dollars on something that will not work effectively and efficiently.
Function:
The design must have a sound purpose for all that inhabit the space(s). It is senseless to spend tens of thousands of dollars on something that will not work effectively and efficiently.
Form:
If a sound purpose of the space(s) can be determined then a design (form) can be created. Many times this goes hand in hand with determining the function. The amount of time spent creating the spaces should not be compromised.
Color:
The last basic characteristic is determining color. This would also include all other materials i.e. windows, appliances, wood species, surface materials etc.
If these characteristics can be satisfied in this order then the client is on the way to a potentially great design.
Who determines "what is a great design?" It is imperative that the inhabitants or client decide what is great or not. Any one of us may really like a space or how it looks visually but if it does not work for those who use it, then it is not a great design. Unfortunately, in an ego driven profession such as architecture sometimes the final result will satisfy only the designer or architect instead of the client. It is the job of the professional to create great ideas and give guidance by listening to the needs of the client, resulting in a great design.
There are a variety of other factors involved depending on the importance of each individual. Most clients want a good memorable experience through the whole process including the building phase. It is not unusual for some clients to look at the positive or negative experience as a factor if they like the space or not. It is also important to have a realistic budget before starting the design, one that is attainable or very close to it. The tendency is to incorporate a lot of fun things or design around a lot of space but if it is not affordable then that could spell trouble. Sometimes it is beneficial to have preliminary drawings made so a contractor could help determine a budget.
Resale value is also an important factor that I take into account always. Many clients want a project with the idea of never moving again or at least living there for many years. In today's environment that can be unrealistic. It is important to incorporate design ideas that include resale values. Keep in mind that you do not want to create the largest or most expensive home in the neighborhood. Also try not to create spaces that are too large, too plentiful or quirky that someone else may not want. That being said, it is important to plan for the day when age or mobility may be a large factor. In that case, the client may want to "age in place" or not move again and designing around that would be a good idea. In conclusion, there are many factors that make up a great design. It comes down to the client not the designer prioritizing wants and needs. It is your space, and with the correct guidance great design will be created. Good luck.