First off, adding creamer and then Splenda to a coffee won't allow you to determine if the coffee itself is good or not. You might be able to tell the difference between obvious faults (over-extracted, under-extracted, bitter, etc.), but the nuances of a good coffee won't be present.
That said, some sugar for some coffees is ok, because some are really sensitive to bitterness.
Now, as to what constitutes a good coffee:
1) Made from fresh beans. Fresh as in 2 weeks or less, on average. Fresh also means no oil on the beans. This is a common misconception. Oil on the bean is not fresh; it's the oils that you want in your coffee, not being oxidized from the surface.
2) Ground fresh right before brewing. Preground is never a good idea except under specific circumstances. Some packaging methods do help preserve preground, but after evacuating all the gas (generally nitrogen) from the container, it begins to stale very, very quickly.
3) Proper temperature. Too cold and it's under-extracted; too hot and you can over-extract. You can moderate this to some degree through extraction time, too hot or too cold will either lead to little flavor or generally a lot of bitterness.
So that's largely preparation method. If you're not preparing it yourself, you can generally tell by taste alone:
1) If it's too bitter, it's not good. A good coffee will have some bitterness because caffeine tastes bitter, but it won't be so insipidly bitter that you can't drink it. Espressos from the majority of coffee shops are not made properly, and you get a lot of bitterness and little else. Also, the roast of the bean will determine much of this. If you overroast the bean, then you literally roast away the coffee oils that help balance the bitterness; all that's left is the char taste of the roast and the bitterness. Nasty.
2) Smooth, generally medium body. The oils will leave a somewhat viscous sensation in your mouth, so it's less watery than you find with most coffees. It should have a heavier body than water or almost a syrup if you're brewing espresso.
3) You should be able to taste more than the roast (sometimes tastes like toast, nuts, bread, etc.). A good bean will have some dried fruitiness to it, sometimes floral, chocolate, carmel, etc. This depends on the bean, roast and preparation method, but the point is that it's more than just the roast and typical coffee flavor.
That's all that immediately comes to mind. I'm typing this fast, so I'm leaving out a lot of things. You also have to realize that taste is always subjective, and what constitutes a good espresso vs. a good drip are going to be vastly different; still, the basic ideas above hold true.
While that may be true - there can be SOME objective standards to taste.
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