I will say that the EU had a ton of things going on in the Star Wars Galaxy. Some are explained and shown in heavy detail...Some that are mentioned or isn't exactly expanded upon.
And this is about the latter.
Which parts of the EU, in your opinion, you wish had a novel (or comic series, etc) that would expand more upon?
Two things came to mind for me, Renegade Squadron and Rahm Kota. Mostly video game related, it's hard to get something out of those two other than their backstory and history in my opinion.
Renegade Squadron had a great set-up, as they are mostly men with shady pasts who don't share the same ideals of the Rebel Alliance but have the skills to take on the Empire. Picked by Han Solo and Col Serra, guys who admit they're not nice people, Renegade Squadron were basically the guys who did the dirty work. Problem is...That they are mostly composed of generic troops in the Battlefront games, so no personality was really there other than hardcore badasses. I would have love to see some material of actual members of the group.
Rahm Kota, the one Jedi who escape Order 66...But nobody really cares to show his exploits in both the PT-Era and even give the man a conclusion. Quinlan Vos, K'Kruhk, A'Sharad Hett, most survivors tend to have some conclusion after Order 66 (Vos's escape, K'Kruhk's society of Jedi refugees, Hett's downfall to Darth Krayt for example). But Kota has always been a sort of random guy who just happened to be there. While one can really say that the Force Unleashed was too out there to really put in the main canon, Kota was in a battlefront series game...So what the heck? Where is his story? Where can we learn his bias on clones? What happened to him in the very end?
But yeah, my two cents of things.