I'd say the Thrawn Trilogy is the single novel set that sets a bar that's difficult for any EU to attain or surpass.
Even what some don't like, I actually enjoyed pretty much... The ending was a tad anti-climactic for me in the aspect of C'Boath and Luuke, but the battle was great...
Zahn set up incredible characters, species, and utilized ALL original characters with a skill that made you envision them like they were right there on the silver screen. I could really visualize Chewie talking to Han even... Again, Zahn's been the ONLY author with any skill enough to utilize Chewbacca in text as well as Lucas utilized him on film. That's a credit to Zahn considering the rest of the hack writers couldn't manage it so they offed the character.
Chewie's highlight is his defense of Leia against the NOghri assassination attempt, I believe. Very good.
That said, Zahn actually put his mind to work, created a military genius as the legitimate threat to the fragile New Republic, and he explained away 14 years of warfare's wearing on the once mighty Empire... He used a lot of military strategy along with his story, and no super weapons, super aliens, or cosmic mysteries...
You can't beat storytelling like that. The military stories often are the most "believable" then, in my opinion...
From the accompanying story to Force Commander, X-Wing, TIE Fighter, XW: Alliance, or Dark Forces/JK (with its more centralized story)... to the X-Wing series of novels and comics... They're some of the superior writing overall in any EU.
In my opinion, poor EU outweighs the good more often than not... The good thing about EU is it's a free-for-all as to what you pick and choose as "Real Star Wars" for your enjoyment. No forced canon of this stuff, it's all debateable if it isn't in the films.
I personally pick through things then... With the NJO I like select aspects, such as the re-establishment of the Jedi Order under Luke's command... and I like how it isn't in line iwth the prequals really. Luke's trying new rules and things (even if it's only because the prequals are only being made now).
At the same time, while I like things in NJO I truly despise others... hack writing tricks like offing a "main" character for the sake of new readership, outright copying (not even masking it well) aspects of Star Trek villains that are popular, etc...
So I pick through things I like when I'm thinking about EU, or thinking of inspiration for something I want to work on in customizing or something along those lines... It's all ok then once I pick it apart.
That said, here's my top EU hates:
-Super weapons... There's too many biological, chemcial, scientific, military weapon, doomsday devices... The World Devastators in Dark Empire 2 (I think) were the start...
-Super beings/villains... The Vong are up there, but Xixor comes in there too. I HATE that someone would even CONSIDER Xixor as plausible given the storyline of Vader and the Emperor... I just hate the thoughts that the EMperor woudl drop Vader for anyone but Luke. There's other crappy villains too, but Xixor really is up there.
-Everyone must tie to everyone else... I hate this.
Every character in the Cantina's a violent felon, or after someone, or doing something they shouldn't... Nobody was just there for a drink on their way elsewhere.
Or, for instance, everyone knows everyone... Dengar's out for Han because Han wrecked him in a race or some **** like that... STUPID! Could it be that Dengar's just a GOOD hunter who is trying to capture a hefty bounty!? Does it have to tie together?
OR...... Just outright blatant stupidity... IG-88 in the DS2 anyone?
-Films Contradicted... Fett lives on (And god knows his further stories are horrid... Dengar's his best man? Where's my F'n gun!?), guys on the Sailbarge all seem to live, Ponda Baba and Evazan live, etc...
Just silliness for the sake of making a sale. No integrity in the story writing, no attempt at legitimately writing something new and interesting...
Just stupid to me. And unfortunately all these problems are plagues in the EU overall... Really, C'Boath and Luuke were veiled "Super villains" too. I didn't mind them... I tried viewing them as actually minor threats compared to how they were written... That, compared to Vader or Palpay, neither of these was a real challenge for Luke. At the same time, I can see it wasn't Zahn's shining moment.