I will admit that my first impression wasn't completely correct. After I did some math I realize that the set is a little better then I originally thought but it still has some serious Itemization problems.
I won't go into all of the math but I have a model that estimates the relative value of each of the stats. I also have also entered all of the raid gear available into a spread sheet to and and then calculate a value for each piece using the relative stat values. I then use this value to rank each of the gear items to come up with a Best in Slot list for each gear slot so that I can make the best gear choices possible.
Anyway, I've inserted the new T8 items into the model to see how they rank in relation to the T7 set and other gear currently available in game. The results were not good.
Let me give you a little back ground before I go into the results.
1. My ranking is purely a DPS ranking. Stam and MP5 have no value in my ranking, and Spirit is only measured in how it converts to Spell Power. I'm not saying those stats don't have value, but they are very hard to quantify.
2. The relative value of stats will change depending on your gear level. The hypothetical moonkin I used had 2900 spell power, 41% crit chance, 29.4% haste before NG, and 99.9% chance to hit. All of these numbers include raid buffs. The hit chance is so high to minimize the marginal value of Hit rating. I also assume that SF is used 75% of the time while Wrath is used 25% of the time.
3. Using the stats above the relative value of stats comes out to Hit Rating = 1.48, Spell Power = 1, Haste Rating = 0.84, Crit Rating = 0.80, Int = 0.35, and Spirit = 0.15. As I said before Stam and Mp5 have no value because they cannot be directly converted into DPS.
In short, Three of the five T7.25 items are better then their equivalent item in T8.25. This is in terms of pure stats. I have excluded the set bonuses from this comparison. The other two items are huge improvements over the T7.25 item and make the entire T8.25 set a little better then the entire T7.25 set.
Here are the Rankings:
Using this quantitative approach to evaluating the gear I come up with mixed conclusions. In total, T8 is better then T7 if you ignore the set bonuses, but how we get there is strange. Here are the stat differences when comparing the Heroic versions of the two tiers:
T8.25 Conqueror's Nightsong Trousers - 325.7606
T8.10 Valorous Nightsong Trousers - 302.6301
T7.25 Valorous Dreamwalker Trousers - 218.9037
T7.10 Heroes' Dreamwalker Trousers - 194.9011
T7.25 Valorous Dreamwalker Cover - 402.1844
T8.25 Conqueror's Nightsong Cover - 393.3498
T8.10 Valorous Nightsong Cover - 373.4473
T7.10 Heroes' Dreamwalker Cover - 353.7805
T7.25 Valorous Dreamwalker Mantle - 216.1341
T7.10 Heroes Dreamwalker Mantle - 188.4584
T8.25 Conqueror's Nightsong Mantle - 179.3919
T8.10 Valorous Nightsong Mantle - 167.2165
T7.25 Valorous Dreamwalkers Vestments - 257.1615
T8.25 Conqueror's Nightsong Vestments - 256.4061
T8.10 Valorous Nightsong Vestments - 239.0354
T7.10 Heroes' Dreamwalker Vestments - 227.6252
T8.25 Conqueror's Nightsong Gloves - 219.1752
T8.10 Valorous Nightsong Gloves - 202.2246
T7.25 Valorous Dreamwalker Gloves - 164.2674
T7.10 Heroes' Dreamwalker Gloves - 147.4499
T8.25 - 1374.084
T8.10 - 1284.554
T7.25 - 1258.651
T7.10 - 1112.215
Int: 394 - 345 = 49 Gain
Stam: 381 - 345 = 36 Gain
Spirit: 216 - 94 = 122 Gain
Crit: 132 - 254 = -122 Loss
Haste: 81 - 122 = -41 Loss
Hit : 176 - 83 = 93 Gain
SP: 542 - 453 = 89 Gain
* T8 is the first number.
As I said above, T8.25 is better the T7.25 in terms of pure stats, but that doesn't mean that T8.25 is as good as it could be. Really, T8.25 is getting its superior ranking more due to the item level of the gear then the itemization on that gear. The T8.25 does have a huge increase in Hit and Spirit, but that is worth 155.94 (93 * 1.48 + 122 * 0.15 = 155.94). On the flip side we loose a lot of Crit and Haste. It is worth 132.04 (122 * 0.80 + 41 * 0.84 = 132.04). As you can see what we gain in hit and Spirit is almost completely wiped out by what we lose in Crit and Haste. So most of improvement in T8.25 comes from in the relatively standard increases in Spell Power and Intelligence.
Another good indication of how poorly designed T8.25 is by comparing looking at the relative difference between T7.25 and T7.10. The Heroic set has an item level 13 above the item level of the normal set. This is the same level difference as level difference between T8.25 and T7.25.
T7.25 has a value of 1258.651, T7.10 has a value of 1112.215. So by going from the normal set to the heroic set you gain 146.436 in value. If Blizzard had just upgraded the T7.25 set with similar stats as the upgrade from the T7.10, then the new heroic set would have a value of 1405.087 instead of 1374.084 from the actual set.
The situation isn't as bad as I originally thought. At first I thought Moonkin might completely skip T8.25 but in actuality T8.25 is an improvement over our Dreamwalker sets. However, that isn't our only option.
The main attraction to gear sets is the set bonuses. If the set bonuses aren't useful then most classes can build a better set out of non tier pieces. The jury is till out on the moonkin T8 Set Bonuses. It looks like the 2T8 bonus is getting increased to 15% (as I suggested. :D ), but the 4T8 is a complete unknown. As it stand right now I wouldn't be surprised if most people skip 4T8 bonus and just use the Hand and the Legs from T8.25. I haven't evaluated all of the new gear in Ulduar, but I am sure that there are better itemized pieces for the other three armor slots.
If Blizz really wants Moonkin to use the full T8 set then they need to change the itemization. The T7 sets are an excellent example of what our set should look like since they are itemized very well.