Everything there seems sensible, but we'll have to see how it plays out. I'm not sure why +6/+12 rather than +5/+10, which are nice divisions of a d20. I am also happy to see the back of the skill dice, let's stick with a d20+X universal mechanic.
And now, a suggestion. The problem with certain effects, such as paralysis and stun, is that the saving throw model insists they be make-or-break. You save, no worries, you don't, goodbye. Could a specific condition not be broken into an ascending scale to represent that condition? My idea is a little like the progression of petrification in 4E, where each failed saving throw would make things worse until you were a nice new piece of decor. A suitable example would be paralysis: stage 1 halves your speed, stage 2 denies you your move action and stage 3 denies you all physical actions. This is basically slow -> immobile -> paralysis. How would it operate in practice? Well, for any given spell or effect, a saving throw would reduce the result by one level - save against ray of frost and you can move fine, save against hold person and you can act but not move. For creatures such as ghouls, they don't paralyse you with a successful attack, they add another stage of the effect if you fail your save. So if a ghoul hits you three times and you save once, you're immobile, save twice and you're slow, and so on. For the duration of effects, you should be able to take a mental action to attempt a saving throw against some effect on you - so if paralysed, you can will yourself back in the game. Obviously this makes stun the most powerful effect as it would deny mental actions, but stuns should (hopefully) never last more than a round.
It gets better though, because you can start to play with the way monsters make saving throws. Legendary creatures don't need their handful of autosaves, simply give them an impressive save bonus, a legendary action to make a saving throw, and locking them down will be hard, but not a waste of time if they save, since you'll still immobilise or slow or something them, you still deny them some action somewhere. It also brings in the idea of lots of low-level guys having a chance against a high-level thing, since a small group of spellcasters could all cast the same spell and effectively make Ray of Frost act to paralyse.