I had a lot of fun during my brief stint as a Sith Inquisitor in Star Wars: The Old Republic. The leveling was great, the storylines were compelling, the instances were interesting, but I eventually went back to World of Warcraft in the end. SW:TOR didn't feel very unique, it didn't have enough to grab me and hold me, to suffocate me with its content and keep me away from Blizzard.
Even so, there were a few differences between Bioware's entry into the MMO space and our site's namesake, one of them being the concept of a server-wide legacy. SW:TOR's legacy system, if incorporated into WoW, could be a great way of introducing leveling bonuses and the like, something WoW has historically done via heirlooms and guild perks. Personally, heirlooms have always left me feeling a bit too overpowered and take some of the fun out of the leveling process -- I've even leveled characters without heirlooms, just because it's more challenging and, thus, rewarding.