Well, after a week of exploring Book 8, I think I can safely say that Turbine have done well by us. I have completed two 3-man and one 6-man instances, and am very happy to report that they are interesting, well-designed and fun. They include a welcome puzzle element, but it's not exorbitant, and is unlikely to baffle the average party for very long. Combat is challenging but not ridiculously difficult, and the specific tactics required to take down the bosses can be worked out after two or three attempts at most. Above all, they can be completed successfully by pretty much any mix of classes; the basic formula remains tank/healer/DPS, but any number of changes can be rung on it, and I don't think any class is likely to be left out in the cold for long.
From the point of view of loot, these three instances (Mirror Halls of Lumul-Nar, Water Wheel and Halls of Crafting) drop Glistening Elf-stones which can be exchanged for the three new tier 1.5 radiance armour pieces (respectively, gloves, leggings and jacket with +15 radiance). You need four stones for the gloves and leggings and seven for the jacket, but the good news is that all participants in these instances get one stone each, every time the final boss is defeated. I haven't yet had a chance to try the new 12-man multi-raid sequence which drops the Greater Elf-stones exchangeable for the tier 2 (+20) radiance armour, but on the strength of what I've seen so far, I'm confident it will be a good one.
Unfortunately there are no new regions to explore (other than the instance dungeons), but then you can't have everything, or at least not all at once. A nice little extra is the fact that several items now stack up to 100 per slot, including crafting materials and potions, thus freeing up quite a few slots in packs and vaults. There are also lots of new decorative trophies to collect; now all we need is for housing to get some care and attention, so that we can actually display them...
All things considered, congratulations are in order.