I have played 6 games against 5 opponents. I have used Dark Elves against VC, Empire, Skaven, Orcs, and Beasts. I am far from an expert, but here are my thoughts.
8th Edition thoughts in general:
Magic is very random, but it's one of the greatest changes they've ever made. Taking a variety of wizards does give you an edge in the magic phase as it should, but not one that is going to make your opponent hate life. With normal rolls and some solid magical support, over the course of a 6 turn game, you should have 2 phases where your magic is very powerful, 2 where it's ok, and 2 where it's pretty underwhelming. That seems about right to me. Additionally, the various "levels" of many spells allows you to compensate for whatever amount of dice you take. It really works amazing. The best endorsement I can give it is this: If you go magic heavy you will deal with some randomness, but it can win the day for you. On the other hand, you can also take no magic and most phases, you won't suffer. It feels, after 6 games granted, incredibly balanced.
The new initiative striking system is very cool. It is really important to have a high initative, and lots of attacks, but it's balanced very nicely by the step up rule, b/c it's even more important to be survivable and whether he's hitting you first, or he's hitting you after you go.
Hordes have some merit, but I don't think you will see a bunch of them long term. I think you will see units of 40, but deployed 5 by 8 rather than 10 by 4. Most units that are cheap enough to field 10 wide, aren't powerful enough to want to field that wide. however, the new magic system, with all it's buffs, could change that a little.
BSB's are the new scroll caddy. You won't take any army without one unless you are an idiot. Even then, you'll probably take one.
The reform rules makes so much more sense. Quick reforms are cool and intuative. The fact that you can reform after winning in combat and chasing units down is great too. It really encourages you to be be aggressive as it doesn't leave you hanging out in the wind with your Driver out. That's so smart
shooting is much more devastating. Shooting in two ranks is amazing. My unit of 10 crossbowman take up a frontage of only 100 mm but pump out 20 shots a turn. That is amazing, and quite fun. This sounds horrible for close combat armies, but....
The board is smaller. The armies start closer together. While this isn't actually true, the ability to march even within 8 inches of an enemy (with a LD test), the fact that your average charge range (for an elf) is 12 where your max charge range use to be a 10, and the ability to do some other things means that you are much closer. I barely lost to RPA's Empire Gunline today. A lot of factors went into that, but a big one was me not just driving forward at his units. I tried to sit at the back, and paid for it for 3 rounds. When I finally moved up, I found i closed the gap quickly.
rolling lots of dice is fun
Terrain rules aren't as stupid as I thought. Forests are much different, but not bad. 2 cavets to this though. 1, I would never play random terrain in a tournament setting, or even in a friendly setting unless playing a buddy I played all the time and 2) the hill rule is stupid. For the NIYF tourny, we played hills as having a height of 1 foot, and a unit being partially on it was able to be seen and see anyone not behind a hill. I suggest everyone do this.
true line of sight is ok, but i Think it's better if you just consider models to have the same height based on base size. I don't like the idea of penalizing conversions or things.
The rules are so much clearer. As I have told many of you, I strongly considered leaving Warhammer for Warmachine b/c I was so fed up with rules disputes, unbalanced armies, and the complete lack of clarity in the rules. I have only played 8th edition 6 times, but I feel like I have so much more understanding and clarity with it, then I ever did with 6th or 7th. Charging is so smooth now. I love how you premeasure, as that way you know the roll you need before you roll the dice. If it's super close, you may dispute what you need, but it happens before the roll. This eliminates so much chippiness and bitterness. Simply measure closest to closest, agree on the roll needed, roll the dice, then move them in. Simple, obvious, and set up to drastically reduce the disputes and bitterness of the old system. I'm not saying I like every rule, nor that everything is crystal clear, but the improvement is much more than signifigant. It's an epic sized improvement, and it makes the game fun. Understanding a game makes it fun. They have made understanding this game much easier, and much more attainable. I love that. I feel like I can confidently list my Warmachine models on Ebay tomorrow and feel good about staying in Warhammer for the foreseeable future, or at least for the next 5 years.