It's a miracle he lived up to 76 regarding his unhealthy lfestyle and recurring heart failures. But on the other hand - alcohol is a highly effective preservative
He was the right man at the right time. Russia was in turmoil and on the edge of collapsing order (coup attempt in the early 90s; the Ruble crash shortly afterwards, etc.)
He might not have been the greatest politician, but look at the alternatives Russia had (Rutskoy, Syuganov, Zhirinovsky). He kept the Federation alive (at the cost of the Chechnya war) and the economy running (at the expense of nepotism and an appalling social structure that is divided into a thin layer of the extremely wealthy and many many very poor people).
Yeltsin's legacy is a mixed bag of minor successes and major problems. But it's the best Russia could have hoped for.
When Putin will pass away some day, the verdict might be quite similar.