I will be frank. Warhammer Online is not the best Massively Multiplayer Online Game (MMO) I've ever played. That isn't to say that it is a bad game, however. Actually, Warhammer has done quite a bit to instill some true fun in the MMO arena of gaming. While there isn't really a whole lot of actual innovation in the game, the developers have carefully crafted something that is actually enjoyable - which is something many MMOs cannot really attest to.
I've played quite a few online games in my time. I've usually had a preference for the open world games that provide a lot of freedom. EVE Online appealed to me because of this with its player-driven content. Warhammer, however, relies more on a carefully crafted theme-park-esque style that guides a player from one point to another. Luckily, that theme-park is actually pretty interesting.
Mythic, the developers of Warhammer, have provided a huge number of quests in the game for players to do. This cuts down heavily on the general experience-grind that many MMOs face, more so during the early levels. You can actually feel like you are accomplishing something as you go from one quest to another, gaining experience and learning about the overarching story of the game. However, as you go up in levels, you'll begin to find that quests only provide so much protection from the grind as your progress begins to slow dramatically. This can make some of the latter levels drag on for a bit longer than you might like.
Along with normal quests, the developers introduced an interesting mechanic: Public Quests (PQs). These allow multiplayer players, regardless if they are in a group or not, to gain experience and rewards by participating in a multi-stage quests that happens in particular areas. This is interesting as it provides a great social mechanism to bring players together under a common goal, working together to complete the quest. It also provides incentive for competition at the same time, as only the top performing characters will get the best prizes. Sadly though, I spent most of my time soloing the early stages of these quests as few others seemed to partake in them.
Yet, even with the content mentioned above, Warhammer's greatest strength is its competitive gameplay. Players are divided into two major camps: the armies of Order and Destruction. These armies are caught in a titanic battle for the fate of reality as they wage massive war on each other. Massive war, quite adequately, pretty much describes Warhammer. In fact, unlike most games, players can engage in combat against other players as soon as they start the game.
When you enter into a Player versus Player (PvP) scenario, you will be matched up against allies and enemies of a similar level range to do combat with and against. This instanced battle will provide an objective that must be completed in order to gain points - that can be anything from capturing zones, capturing flags, holding artifacts for a certain amount of time, and, of course, killing other players. Each level range has several different types of scenarios, and players can actually advance their level significantly by participating in them. These scenarios are certainly quite a bit of fun - but they can occasionally get very one-sided and the enjoyment worn out after too many plays.
Besides scenarios, players can travel into the massive persistent battlefields that are located in each zone of the world. Here they can team up with fellow players to lay siege to enemy castles and claim them for their own. These battles, while sadly not always common, can be massive events involving huge numbers of players on both sides, complete with siege equipment. This is where Warhammer truly shines as a game.
In the end, it isn't perfect. It can feel a bit "grindy" in later levels, PvP scenarios can be worn out a bit too quickly at times, and the open field castle sieges are not always common, but the game itself is certainly worth a try if you enjoy MMOs in general - and more so if you're a lover of PvP.