Whilst there are some interesting things to see in Lima, it is very difficult to believe that the city deserves its WHS status. The Monastary of San Francisco is very interesting, but much else stands out.
There are plenty of old colonial cities on the WHS list, and there are plenty that are not that are much nicer than Lima.
However, for WHS list tickers it is an easy site to 'bag' as it is the gateway for the rest of Peru, and the other sites in this wonderful country are magnificent!