I've got only the few days north of Johnson left to go and I've done all my hiking earlier in the summer. Here are a couple of good websites to check out:
Long Trail Hiking
Green Mountain Club
Expect mud. Do not expect bog bridges over the mud.
There are several sections that have a reputation for being dry but having done most of my LT hiking during rainy summers I haven't had any issue with getting enough water. Unless we have a drought for the rest of this summer you'll likely be fine. I'm having a hard time imagining a dry Long Trail but apparently it can happen.
Most of the shelters are in very good condition and recent pictures for most can be found on Whiteblaze and on Long Trail Hiking.
North of Maine Junction you'll have a lot less company in general but you'll likely see a lot of day hikers and weekenders along the higher ridges. Hiking in late June and early July I've not often had to share a shelter but I think usage is higher in August. Some of the shelters charge a fee ($5) and they are noted on GMC's website as well as in many of the shelters along the Trail.
As Hillwalker mentioned, the terrain in the northern half is very different from the easy, rolling terrain in the south. That said, I didn't really find it to be any crazier than climbing in the Pressies or the Mahoosucs with one exception. I find Vermont bedrock to be a lot slicker, especially when wet, which I've almost always found it to be. That is what has been most challenging in the north for me.
-vegematic