I will compile some information here:
1) When you hit a monster in castlevania in most cases 4 things happens, the monster flashes, a sprite is shown (something like a X) in the place where you have hit, and also, in some cases a sprite with some sort of effect is also show (like blood or a explosion), and also a sound is played.
This 4 things that happens creates a sense of being powerful, a good combat feel.
2) When you get hit by a monster your character enter in a 'pain' state, which can be different based on what has hit you.
If you walk across a monster, this pain state is very short, but when you get hit by a projectile, your character generaly is thrown back and the pain state duration is big.
3) There is some kinds of monster:
Paper: they are like the zombies that emerges from the ground, these kind of monster are killed super fast, with like 1 or 2 hits.
Annoying: They generally fly, or dance, or do some sort of unexpected movement.
Trick/Hard: They are like those giants tha throws you a ball attached with a chain, they are slow, they have much life, and do lots of damages.
Shooters: They're like the skeletal archers, and some of them don't even move, like the skeleton head that is always attached to some sort of wall or floor.
4) The game has very limited heal mechanics and the save points (which restores HP) are a few in the map, so, at the same time you can afford to take some hits, you have to be careful to not take damage for nothing, you never know how far is the next save point.
5) The powers and skills that are good, generally comes to complement the main melee attack, the powers that compete with the normal attack usually don't worth using because the damage does not make that difference, what makes difference and makes a power appealing its the area of the effect, the utility and the speed. For example, the Soul Steal in SoTN is a power that is good by its utility, it can heals you, and also can hit many monster. The tetra spirit from SoTN is good by its area of effect, since it can hit 4 different monsters speeding you progress through the game. The knife you can throw is another good power because it is fast and it can reach monster that are far away. So the powers are not about the damage, they are about making you progress faster, and to kill things that are hard to hit with normal melee attack.
6) The breakables like torches that can drops small things are very important, since you will be walking again and again in the same scenarios for many times, it distracts you a bit and proposes something to interact and because you have to jump and attack, it makes less boring the patterns that the rooms have. If you have just a empty room, you just walk straight to right, but if you have an empty room with a breakable candle, you have to walk to right then jump attack then walk right again. This combined with some platforms can create a better feeling about the game, and it also rewards you for doing so.
7) Ducking is a considerable feature, it adds a simple depth to the combat. You now have more than one option to react for the same situation, like when a projectile is shoot in line at you (you can jump or duck). You also became more flexible in the combat and when it comes to practice, making different moves and reacting in different forms makes the players feels rewarded in the sense "I'm a better player, I can do that sort of cool moves, I can dodge many things".
It adds too a new attacking strategy, you can duck at the foot of a shooter monster, and attack it, otherwise you would have to jump its attack then when you land you would perform a normal attack. So, ducking is simple but it adds a new layer of moves and decisions to make while in combat.