In an era before I owned all the episodes on blu-ray (or DVD or VHS) it was a window into parts of the ST universe syndication had yet to show me. Plus, it had famous comic artists doing Star Trek characters. Check out the cover above by Howard Chaykin. Or these Orions by Todd McFarlane:
How about Talosians by Bill Wray?
There's also stuff by Walt Simonson, Gray Morrow, John Byrne, and Ron Frenz there, among others. It's well-worth tracking down a copy.