Quoted By:
The impression I get is that besides a sadistic side, Alucard also bears a masochistic or/and self-punishing side, in how he frequently leaves himself open for an enemy to get the first strike in, and often a damn good one too (.webm related is on the low end), to then reconstitute himself as to watch the smug color drain away from their faces, coming back to the sadistic end of it all.
Clearly he revels in the pain, perhaps in a similar way to how someone who self-harms revels in the endorphin release and the punishment for what they hate about themselves.
There's a lot he seems to regret about how he lived mortal life, and over what he would become.
Just as well, he clearly seeks out people who can match him in battle, hence his great disappointment at Luke Valentine being not all that much more than big words (and how he sounds so betrayed and disappointed when he realizes, as if he was just cheated on by a lover), in addition to his strong affinity for Alexander Anderson, then particularly his sorrow over Alexander surrendering his humanity to try to match him.
No doubt he wants to probe every opponent who seems even remotely promising to see if they can actually thrill him in combat.