IMO, the following are absolute tripe:

Truce at Bakura, The Courtship of Princess Leia, Tatooine Ghost [<-- Oh dear Lord, this one was awful; worst Star Wars book I've ever read], The Crystal Star.

However, Zahn's books are, for the most part, excellent--especially the Heir to the Empire trilogy. (I found Survivor's Quest and Outbound Flight a little lackluster compared with his other books, but they're still palatable.) Also, the Rogue Squadron and Wraith Squadron books are superb. I recommend all of them extremely highly, as well as I, Jedi. There are eleven total, counting I, Jedi, but I haven't yet read the most recent one (Mercy Kill), so I can't comment on it.

The Jedi Academy Trilogy are sort of in a category all their own. On the one hand, they are quite important insofar as the EU metanarrative is concerned. On the other hand, even though the overall storyline is pretty solid, they're remarkably poorly-written (though not as infuriatingly bad as the four afore-mentioned shite-biscuits). Maybe give them a try, but don't feel bad if you give up halfway through.

And DuracellEnergizer, you are remembering incorrectly; Luke does indeed disguise his face through the force in Crystal Star.