Liwonde National Park is Malawi's best for Wildlife. But you can also see plenty of elephant, impala water buck, and baboons. Less common are sable, kudu and bushbuck and the bird life, being on a river, is also plentiful.
Leopards exist and can be spotted on the night drives.
However, it's the sort of park where one day you can see nothing one day and everything the next, it really is pot luck. Viewing is far better in the dry season - especially at the end of the river as many of the larger animals come down to drink. During the rains it is very difficult to see much at all.