1. Arc couldn’t kill Roa, because he kept reincarnating so even if she killed his current host, he’d just reincarnate into another one. Shiki was able to kill Roa because Shiki’s Mystic Eyes of Death Perception (MEoDP from now on) destroy a person’s existence as well as their body. So once Roa’s existence was erased, he was no longer able to reincarnate.

2. Arcueid was already weakened from when Shiki murdered her, so she didn’t have enough strength to regenerate a second time. At least, not without drinking blood, which she swore she’d never do. This leads to her sealing herself away for all eternity since she wouldn’t be able to live without blood.

3. Shiki’s power comes from when SHIKI killed him when he was a child. Shiki was saved by Akiha, who shared half her life with him, which is why Shiki is so weak. I don’t know if they went into this in the anime, but SHIKI is Akiha’s real brother and lived with Shiki, who was adopted, and Akiha in the Tohno mansion. I don’t think Shiki’s power goes to anybody who has a near-fatal accident, though. Probably only to people who have high magical potential.

Shiki was actually born into the Nanaya family which is why his knife has Nanatsu-Yoru/Nanaya carved into it. This is where his “killier instinct” comes from. His family was a group of highly trained assassins who killed anything non-human. Because of this, Makihisa Tohno (Akiha’s father) had them all killed, except for Shiki. The only reason he spared Shiki and adopted him, was because Makihisa’s son shared his name (SHIKI). Whenever Shiki is around something non-human or is in mortal danger, his Nanaya blood commands him to kill his enemy. When his Nanaya blood takes over, it allows him to have greatly enhanced strength, speed, reflexes and all the skills of a highly trained killer.

SHIKI/Roa shares the MEoDP with Shiki because their minds are connected and have been since the day SHIKI killed Shiki. However, SHIKI’s MEoDP work differently than Shiki’s. I think SHIKI’s eyes see what makes the person live, while Shiki’s eyes see what makes the person die. In other words, SHIKI can cause the death of things while Shiki can cause them to stop existing (by stabbing the points of death, not slicing the lines). In fact, I don’t think SHIKI can even see the points of death.

4. Kohaku gives him the knife, saying that it’s from Makihisa. Makihisa took the knife from the Nanaya household once he had them killed and kept it in his room. Kohaku took it and gave it to Shiki.

Here are my recommendations.
I left stuff off the list if I didn’t see it, or if I didn’t like the way it turned out.

2005
Saishuuheiki Kanojo - Another Love Song (read manga. didn’t see anime)
Angel Heart (good adaptation of manga)

2006
Fate/stay night (differs from the game)
Code Geass Hangyaku no Lelouch (supernatural+strategy+mecha)
Utawarerumono (fantasy + interesting character designs + crappy ending, but still worth seeing for the earlier eps)
Suzumiya Haruhi no Yuuutsu (didn’t see it. heard it was TEH BEST EVAR)
Ray the Animation (*cough*blackjack*cough*)
Saiunkoku Monogatari (spiritual successor to fushigi yuugi?)
Red Garden (heard it was good)

As for your list,
* Black Jack TV (ep 1-30)
got tired half way through.
* Black Jack 21
watched it all. wished for more.
* Honey and Clover (watching, at episode 13)
tired of it.

* Mushishi
skipped
* Black Lagoon
1st ep only
* Blood+
30 eps and quit
* Koukyoushi Hen: Eureka Seven
1st ep and quit
* Ergo Proxy
never tried
* Nodame Cantabile
read manga. assume music is good. no desire to see anime.

Might watch list:

* Kamisama Kazoku
no idea.
* Shakugan no Shana
saw an episode or two. interesting premise, but character interaction feels a bit cliched.
* Le Chevalier D`Eon
no desire to see this.

***SPOILER WARNING***

About the hype… Yes, I do watch more well-known movies, since I usually go with friends to movies. It’s really hard to persuade them to go see movies like A Scanner Darkly or Thank You for Smoking (I saw it alone). I need more friends who likes to see Independent movies and such.