Warhammer Online is the first MMORPG since World of Warcraft was released that actually holds a candle to it in terms of content. Generally, companies have launched MMOs without certain features, promising to add them in the future. This hasn't been too successful, because WoW players would come, see an incomplete game, and leave. Warhammer isn't an incomplete game, and the upcoming Wrath of the Lich King expansion to World of Warcraft is doing more catching up to WAR than WAR is to it.
The fan base is growing, and it appears that people are staying – happy to find a new home outside of Azeroth. Warhammer Online is definitely worth a try for anyone looking for an alternative.