You don't need to read COTJ to read Darksaber- they're both standalones and DS summarizes what you need to know about COTJ to follow it's plot. COTJ is a mixed title at best- it has some interesting "not sure what they'll run into around the corner" moments, but overall is generally lacking. Darksaber is a little fun, though. You have the kinda neat element of Daala and Pellaeon joining forces (which, at the time, helped make the post-ROTJ era fele like it was coming together, as now you're fusing elements of TTT, DE & JAT into one story), as well as a mini-tour back to places from the OT, getting to see how they've changed since we last saw them. Additionally, the main Hutt/Death Star plans plot has a cool post-Soviet-fall-nukes parallel vibe that i rather enjoyed, and the whole Darksaber concept itself really makes a lot of design sense. I also liked the insights into the history between Palpatine and Bevel. Another noteworthy aspect is that it's very much a psuedo-sequel of sorts to the JAT and it's characters.