I'm just reading Thrawn Trilogy at the moment FOR THE FIRST TIME (not kidding) so my observations don't fit neither minuses nor pluses that titles of both threads on EU suggest. I even found Zahn's page on Facebook and posted a comment on this matter there, so in order not to write my opinion from scratch I'll just copy/paste it because it's the essence of what I feel about his Trilogy:
I had heard a lot about the Thrawn Trilogy as of some kind of masterpiece recapturing the spirit of SW movies (The Original Trilogy, of course) and was intrigued enough to read it by myself. So my general impression is a mixed bag: it indeed has many strong points and plot twists and captures attention astrain. I don't know, maybe I'm too subjective cause my fav arc has been that of Han/Leia and the scenes that depicted her pregnancy, her intimate communication with the unborn twins and especially the one where she finally gives birth to them was particularly touching and impressive as was the single scene of Obi Wan telling Luke Farewell during his (Luke's) Vision/Dream. The characterization of Thrawn hits the mark. However, some dubious decisions beginning with selecting hardly pronounced names of species, creatures and humans (ysalamiri, vrkhrs or whatever, Noghri, Joruus C'Baoth) that were not typical for SW universe with its easy to remember ones (I can barely imagine Carrie, Mark and Harrison uttering it without them sarcastically grinning or loudly laughing) and ending with the idea that some animal could develop ability to deflect the Force took the shine off and it seems these ideas came from some other world more in the style of Tolkien rather than that of Star Wars. Also what is "a Dark Jedi"? We had been supposed to think relying on movies that Luke was the last Jedi with only a potential hidden in Leia as his sister, because other Jedis were exterminated. The concept of the Force that could be present in a cloned Jedi sounds ridiculous as if the soul of a human being could be reproduced in a cloned unit. Besides, the very word combination "Dark Jedi" is similar to "round square": how is that a Jedi could be "Dark". He's a Sith in this case. Some dialogue exchanges between the characters sounded chilly and overstrained as if borrowed from the lexis of kids playing SW in sandpit. Lando's arc could be more elaborated and self-reliant, tied with the New Republic; hell, we know him as "a gambler","a Universal scoundrel" as Han had described him and it would be awesome to learn much MUCH more of his shady dealings than simply working for the glory of the New Republic just because he once was called up for military service as an Alliance general. Have no doubts he would later rejected this in order to get his hands free once he got done with the Empire. He could've been a trusted friend and a loyal ally to Han Solo, who in turn - logically - could've occupied the position of the Chief of the Republican Intelligence of some kind (like Edgar Hoover - the Chief of FBI) with a rank of General. Also, Han and Leia should've had some more deeply intimate moments than just banal "OKAY, I love you Han" (him responding "I know" that - together with such replies as "don't tell me the odds", calling Threepio "goldenrod" that looked like a rehash of the movies: was it so difficult to invent some original and memorable lines for him to say that would fit his individuality?), maybe show them making love (I mean "making love", not "f'*cking") unparalleled comparing to ordinary human expression in ability to penetrate in each other's souls that the Force (shared by Leia with Luke) would make possible. You made an attempt to show her attachment to him ("she missed Han terribly") but you in no way show us it clearly (when he arrived from his mission, for instance) and all that we have is just expressed using limited range of verbs ("squeezed his hand", "made her face", "lopsided grin"). And the end as for the entire trilogy wasn't so proper, but rather abrupt. In ROTJ we saw all the main protagonists as well as antagonists brought together. But at the end of of the Last Command it's just Luke and Mara and after the final clash with that "Dark Jedi" there were no mention neither of wounded Han, Leia, the twins nor of Republican govt, subsequent events, following the defeat of the Imperial fleet (what happened to it, Pellaeon etc). Overall, it was not a bad try but definitely too insufficient to serve as a basis for the Sequel Trilogy.