I have never played a Castlevania game, but I understand this game is a completely different take on the series. It abandons the Metroidvania style gameplay and uses mechanics seen in modern action games like Devil May Cry 4 and Darksiders. The gameplay is a mix of hack-and-slash, light puzzles and lots of climbing.
You take the role as Gabriel Belmont, a warrior of the Brotherhood of Light. Gabriel learns of the God Mask, a powerful relic which allegedly has the ability to resurrect the dead. He desires it with the hope he can bring back his recently murdered wife. He finds fellow Brotherhood member Zobek (voiced by Patrick Stewart) who is willing to help Gabriel battle evil, but they travel separately. Zobek also provides the narration between the levels.
The camera is fixed which generally guides you in the right direction. When the camera changes, it can throw your direction off, so sometimes you have to let go of the control stick to reset your direction. In combat, sometimes enemies linger off screen and can charge at you without warning. Other times I found the camera was zoomed out too much which meant the enemies were hard to spot. An alternate solution to this would be not to make the enemies a similar colour to the scenery which was a problem early in the game.
Branching paths are rare, so the levels are pretty linear. You are pushed down corridors, occasionally stopping for arena battles before proceeding. Despite the linearity, it's easy to be temporarily baffled where to go. For example, sometimes it looks like you can drop down to a platform, but instead will meet your death. Other sections you think you can reach a grappling point but must ascend/descend slightly further. Conversely, it looks like points are out of your reach, but Gabriel will be able to reach it. The inconsistency of the climbing was often infuriating.
In terms of climbing, there's ledges to grab hold of, a grappling hook is used to rappel up and down cliffs, and swing across gaps. There's the occasional timed jump, but usually you can navigate without any pressure.
In terms of combat, the X button performs basic attacks Y performs a weaker attack but is better for crowd control. B uses special items, A jumps, Left trigger blocks (or rolls when combined with a direction), and Right Trigger grabs. Gabriel doesn't have much health, so you need to be careful not to take many hits. Death in combat will take you back to a checkpoint, whereas death during platforming will respawn you with a small health penalty.
Shortly into the game, you are given a pair of magic meters; light and shadow magic. Weirdly, Gabriel is shrouded in a shadow when using Light magic, and looks on fire for Shadow magic; the opposite of what you expect. Light magic heals Gabriel while Shadow magic buffs his attack power. While either magic is in use, you cannot earn magic from defeated enemies, or increase your Focus meter. The Focus meter increases when attacking enemies without taking a hit. Once enemies are killed, they will drop magic if the Focus meter has reached its limit. It is quite awkward to collect magic, because you must click the left or right stick in to add to your Light or Shadow pool respectively. Trying to collect them when surrounded by enemies is almost guaranteed to end in you being hit.
There's a couple of boss battles against massive Titans where you must climb up them to smash weak points. Sometimes the Titan tries to shake you off and you must hold the Right Trigger to hold on. These battles are extremely slow and tedious; I despised these. There's plenty of standard boss battles too which involve the usual attacking and dodging at the correct times. There's a quick-time-event to finish the boss off. If you get the event wrong, you take a hit, and the boss regenerates health. This was also infuriating. However, there are check-points during the boss battles so you don't have to do the entire fight again.
At the end of the levels, you are given extra points to spend on unlocking new moves. As you progress through the game, you also gain access to special items: daggers, crystal (which summons a demon to damage all on-screen enemies), fairies, and holy water. Enemies can have weaknesses/resistances to these items, and each one can be modified by a particular magic. For example, Light Magic and Holy Water creates a shield, Shadow Magic and Dagger creates a more powerful dagger.
Some of the larger enemies like spiders, wargs and warthogs are ridable. You must wear down their health until they are stunned, then perform a simple quick-time-event to mount them. Usually, when you come across these enemies, you are required to use them to progress. Spiders can create bridges, Wargs can climb certain areas, and Warthogs can charge down gates.
You can replay levels to try and collect all the upgrades, but I didn't feel the levels were fun enough to play a second time, plus the game was long enough without extending the playtime further; it comes on 2 discs!
When the game is this long, you do expect a great story, but the story doesn't seem to develop at all. There's an event within the first quarter of the game that should really unsettle Gabriel, but it doesn't appear to change him. The narration keeps mentioning how Gabriel is filled with rage but he always appears calm. At the end of the game, you are given the predictable plot twist, then a more unpredictable one, with a major unexplained reveal in a post-credits sequence.
Overall, I didn't enjoy Castlevania Lords of Shadow. The mechanics have been done better in other games, it was often frustrating to play, and the story's ideas seem to be thrown at you during the ending, rather than developed across the long playtime.