Phantasy Star 0 is actually quite good; despite the small amount of content that the game provides. If you have played PSO; then starting 0 will be easy as much of the mechanics are similar.

There are 14 classes in 0 (Humarl & Nunewn being the 2 new classes)

The online aspects of the game was free to play; however Nintendo shut the official service a few years back. However I believe there is a hack that will allow you to still play online. This requires a use of an AR device which can be hard to find.

If you have any questions: please post then in the appropriate area.