nah the game aint properly playable. it needs something in jabos plugin to prevent the slowdowns. so if jabos does make the game compatible on his next plugin, then u will see improvements.
however, in the meantime u can get some better gfx out of the game by selecting normal blending in the video settings using jabos 1.3 . also try using the expansion pak, it speeded things up loadz, but crashed for me at one point. maybe there's a way of bypassing the crash.
A lot of things are probaly going to get fixed for the next release of pj64, with Mario Tennis hopefully being one of them. But since their are other improvements one shouldn´t expect to much, it will only lead to disappointment. But as I see it all things being fixed are extra, Jabo´s video plugin is in it recent stage way beyond all other video plugins. And with Azimer giving his full attention to audio the next months are surely going to be something special.
I haven´t cared to check this but is anyone else getting lightning on the screen every now and then when playing Mario Tennis, the lightning is inside a black box and is accomplished by really bad audio. This is of couse a result of Mario Tennis not being supported by Jabo´s plugin. And for anyone not knowing this, don´t press the start button while playing it will cause a error in the video plugin.