The big differences are (1) the Global Explorer is mileage-limited while the Oneworld Explorer isn't, and (2) the Global Explorer allows travel on some additional airlines, namely Air Pacific, Gulf Air and Aer Lingus, plus QF codeshares on some others, including Air Tahiti Nui and South African between Perth and Joburg. There are several additional restrictions with the GlobEx, such as stopover limits and so on, but those are the big ones. For limited itineraries that include Australia/NZ, the lower mileage-limited GlobEx tickets (e.g. 26,000 miles/economy) can be cheaper than the least-expensive OWE, due to the OWE requiring that a minimum of 4 continents be purchased. However, if travel becomes more extensive - say by including South America or Africa, then the OWE quickly becomes better value.

You can do a good comparison using the information on the Oneworld website under "air travel options."