Dark Forces II is way superior to both sequels story wise, but mechanics of both sequels are much better. Kinda like Morrowind>Oblivion>Skyrim. What made DFII: Jedi Knight special is level design that screams Star Wars, with huge levels (vertical design everywhere) with ton of enemies, much variety while staying true to SW lore; original soundtrack and sound effects and of course, story with many interesting villains and main protagonist who is basically a mix of Luke Skywalker and Han Solo, coolest characters in original SW trilogy. Sequels lack these features because they weren't developed by internal Lucas Arts studios. Also, expansion lost some of the charm because FMV cut-scenes were replaced by in-engine cut-scenes. Those B grade actors were a bit cheesy, but still did a wonderful job portraying SW characters, especially Jason Court.
Outcast and Academy have awful story. Outcast has some lame lizard as main villain and Academy makes no sense, with Luke showing up (supposedly buddy of Katarn which is major LOL).