I've played it for a while, just before it was put on steam. I would say it does have replayability, but only until you get tired of sandboxing yourself into all the planets. When they make it so you have limited monetary income, not just science, I will enjoy it more. Mods make the replayability better though.
Right now I recently restarted, and have the Remotetech mod and life support (as well as many others) and I spammed satalite missions around the planets with geostationary orbits. Next up is getting kerbals to survive trips.
(mobile)