At the time of this writing, Michael Phelps just got his 22nd gold medal and New Zealand's Eric Murray and Hamish Bond got the 43rd New Zealand gold medal ever. In other words, if Phelps was a Kiwi, he would have more than half of the gold medals won by the country since the first Kiwis competed in 1920 (though a few Kiwis competed for Great Britain and Australasia in earlier Olympics).
New Zealand fairs much better in the Summer games than the Winter games. The only Winter Olympic medal for New Zealand was a silver won in 1992 by Annelise Coberger for alpine skiing. She was the first medalist from the Southern Hemisphere in the Winter Olympics.
New Zealand's biggest strength comes in boating of all kinds, having won a medal in rowing, canoeing, kayaking, or sailing in all but 2 Olympics since 1956. 49 of New Zealand's 106 medals have been from these sports.
The Olympics of 1900 had only 95 events in 20 different sports. The Rio Olympics has 306 events in 35 sports. Only athletics, swimming, cycling, fencing and gymnastics have been in each modern Olympic games.
In a ranking of Olympic medals per million people, New Zealand comes in 12th with 23.7 medals per million Kiwis. However, the top 10 is primarily populated by countries with high Winter Olympics medal counts. So far in the Rio Olympics, New Zealand ranks 2nd in medals per capita, just behind Slovenia.