Actually he summed up a good answer very well.
At any rate, you can find the answers you are probably looking for if you search the forums for "average K/D ratio," as it's been brought up before.
If that's too much trouble, it could be that the answer is much lower than you would think. If you were to ask most people here, they'd say "good," would be in the 2's or 3's, but that's not really representative of the 500,000 people that play at a given time.
The majority of players are upside down on their KDR. (<1.0) If you can maintain >1.0 you're doing better than the majority of players. Is that good? Well...it's a subjective term when you really think about it, isn't it? If we compare to ALL players, then yes. But surely garnering a >1.0 isn't as impressive as doing it in a League with premiere players, is it?
Of course, this argument doesn't stop here. You have to factor in play style. A person may have played for 20 hrs and have a KDR of 4.0, but a SPM of about 100 or less. So you look at their stats, and see they have 100 kills and 25 deaths in that 20 hours. So clearly, they go 2-1 and run and hide for the duration of the matches. (To the chagrin of all their teammates.)
I'm not sure it's a question that can be satisfactorily quantified with any given values or logic. So really, you have to return to the original answer. Play the game and have fun. Don't worry about those numbers, because they don't mean anything.