Avatar is great, it was what introduced me to the wider world of Trek Lit outside of the New Frontier series, which up to that point had been the only adult Star Trek books I had read. It also helped to start what I now call the Novelverse, the big interconnected modern Star Trek novel (and short story and a few comics) universe. I think there might have been a few connected books before them, but things really took off with the Avatar duology and the DS9 Relaunch.