Like Nizwiz I only do SP as well, but I liked JA more than JO. I do agree that it felt different at first for some reason even though most of the single saber moves are the same. Just something a little different between the two.
I liked the new models that came with the game, the new saber styles (duals and staff), and improved lightsaber effects (dynamic glow). There is lots of things to do in JA modding that are simple to do. Like changing characters and sabers in game instead of having to deal with Kyle replacements. There is saber editing that lets you change values and moves for particular sabers; think like a role-playing game with +1 attack, or +1 defense and such.
Thing is JA is getting harder to find now days. You'll have to order it online most likely. You should be able to find it reasonably priced though.
But like Nizwiz said there are plenty of SP and MP mods that can keep you entertained for awhile. Heck Mercenary is still making his SP maps.