I've only played the Beta for a few hours now as my brother generously let me log on his account and make an 85 Dk (I don't care about stats, numbers, and all the technical crap.. I'm just seeing if playing a Dk is still enjoyable for me) and my very initial impressions from a PVP perspective, just from doing a few random bg's and duel's outside SW, is that self-healing is pretty ridiculous for any class that has a new self-healing ability. I was facing a mage, and the duel was just going on and on and on, whereupon the Mage asked how I was healing so damn much (I was more or less spamming Conversion whenever I saw the opportunity) whereupon I asked why seemingly 9/10 of my attacks were being constantly absorbed (she said she was spamming some ability whose name I can't remember now) It didn't help that when I was finally getting on top the game crashed and I couldn't log back in for a few minutes.
Similarly, it felt like that for every time I fought a Warlock, I had to fight them for a good 30 seconds/1 minute before all their cooldowns were blown and I could finally actually start doing so meaningful damage. On the upside though, I've duelled two rogues and owned them both with ease. But overall, Conversion at least is reminiscent of rogue recup, only the heals it provides are better. I know its only the beta and things are subject to change yet, but I can see a huge nerf coming for that particular talent purely because half a dozen people have stopped the duels I've been in to ask why they're not doing any damage. Death Siphon was similar, only it provided less heals. Conversion was the easy choice in regards to having strong self heals without a cd.
In terms of frost now being "clunky," I didn't really notice. With Runic Corruption, and so long as I played things right, it always felt as though I had something to hit, and my damage was solid. RP generation in Frost Presence is insane and so even while Conversion is active I still have enough for my core attacks, EXCEPT for if I was careless with my Frost Strikes whilst Conversion was eating up my RP. I really didn't notice the 1.5 global cd only because the fights themselves lasted quite long and seemed rather well paced, and not nearly so one-sided as in Cata, e.g., I not only felt I stood a decent chance against rogues and frost mages, I actually beat them.
I tried Blood spec as well, and it felt practically the same as in Cata, although with Runic Corruption, it felt as though I was less at risk of running out of Death Strikes at those optimal moments, so that was good. I very briefly tried Unholy, and it felt more or less the same as in Cata also, although I am less versed with Unholy and it's play style.
So far, the only real problem I can see is having space on my keyboard for some of those new abilities. In Cata I was pretty much set on my keybinds, but now I have to not so much reorganise them, but find space for Unholy Blight, Death's advance, Soul Reaper, and eventually the tier 90 talents. My fingers can only reach so many buttons so fast. And I'm not terribly sure I'm sold on the idea of blizz making us choose between talent options, as only playing for a brief time its fairly clear to me which to choose and why.
Conversion is better self-heals than Death Siphon but Death Siphon does damage. The choice is clear to me: Either you choose an ability that heals more and does no damage or ability that heals less but does damage.