The first and most surprising news, for me, is that the rewards within the instance are on par with those from a 10-man Naxxramas run. The authors have graced us with some solid data and even screenshots of the rewarded items. Items are on level 200, which is consistent with naxx10 and seems they are fitting a nice niche, left by Naxxramas itself.
For one, any plate wearer dps, from warrior to paladin and to death knight, will be pleased to learn that getting an epic helm is no longer so difficult. Personally, I tried in vein to hunt for the tier 7 helm, never ever winning the role if it came up for grabs, and I ended up running all the way to Ulduar before a suitable replacement for my Tempered Titansteel Helm dropped. But now, we have a newcomer, Mask of the Violent Fray and it looks great.
The test crew reported the challenges to have been very easy for them, in fully geared tier 8 sets, so the encounters are, in all likelyhood designed for that same level, naxx10, which on itself of course makes sense. Would be very silly otherwise. Both the report and item gallery are available, so if you're curious, suggest you take a look.
I cannot wait to get a crack at it.