I'm still making my way through Vampyr. I estimate I'm at the 80% mark or so. I think there's two major reasons it's taking me so long. First, I'm very under-leveled due to the whole not eating people thing, and I'm not particularly skilled with twitch mechanics, so boss fights take me a long time to beat. In hindsight, I probably should have played the game on Story. Though I rather think I would have missed much of the "point" of the game that way.
Second, there's a lot of conversations and puzzles with the citizens that I'm really enjoying, and that eats up a lot of time.
I thought I'd discuss the mechanics of the game. They're nothing greatly out of the ordinary, but they work well together.
There are three resources in combat: health, stamina, and blood. Swinging your weapon costs stamina, as does dodging. If you aren't attacking, stamina recovers fairly quickly. Blood powers your vampire abilities, which includes a healing ability, an attack, a defensive, mobility and a special on a long cooldown.
Enemies have two resources: health and a "stun" meter. Certain weapons (like clubs or stakes) can inflict stun damage, as can timing a parry correctly. If you reduce the stun meter to zero, the enemy is stunned and you can bite them and drink some blood, increasing your blood meter. Once they come out of the stun, the stun meter goes back to full.
So combat basically follows a pattern of dodging and parrying enemy attacks, getting some damage in, stunning and biting, then using the blood to heal up and use vampire abilities, and repeat.
One other mechanic is that while you are biting someone, any other opponents won't attack you. That makes it a nice break to allow your stamina to regenerate. I'm not entirely sure if this makes sense from a logical perspective (after all, wouldn't you attack the vampire to save your friend?) but it does allow the whole cycle to actually work. Otherwise biting someone in combat would be an automatic loss.
There are other options. For example, you can alter certain weapons to drain blood, so you don't need to stun and bite. Not every weapon can parry. Some weapons are fast and some are slow. There are firearms, which do a lot of damage, but because of the time period they don't hold a lot of ammunition, so you get very few shots off.
Bosses have a lot of health, and if you get caught by them, they tend to deal a lot of damage in quick succession. A boss fight can be going reasonably well, and then you make one mistake and you lose 60% of your health in short succession, especially if you get knocked down. At least for me, most of the blood drained goes toward constantly healing myself.
All in all, the combat mechanics work well together, there's a nice flow, and they reinforce the whole vampire aspect of the game.