It is based on the famous log4j package from the Java world, and from uses of this package I have seen on customer sites, I feel that it carries a lot of useless baggage, and is - in my opinion - significantly less of a good match than Monolog for Drupal 8.
Monolog vs log4php : equivalences
There is some degree of equivalence between the Monolog and log4php components:
|Log an event||Logger||Logger||Very similar|
|Store an event||Handler||Appender||both can be chained, group, control bubbling (Monolog) / filtering (log4php)|
|Format an event representation||Formatter||Layout||log4php layouts can format a group of events, Monolog formatters format an individual event|
|Massage event data||Processor||Renderer||Not so similar. Monolog processors will often add extra data, while log4php Renderers are typically used to format non-string events as strings.|