Okay, I played a fair bit of the Preview Weekend and messed around with most of the classes available. By no means is this a complete review since I haven't played a whole lot, but I did play enough to get several characters (and I mean several) out of the newbie areas and get a feel for where they were going. Did I get into the second tier of content? No, but I got close to it with several classes.
Here are a number of things I noted...
Public Quests - these are neat though I seem to always roll really low even when I finish in first place, which actually seems to be easier to do than I'd expect.
Models - the models are pretty good. The seem to have more polygons than WoW does and they suit the IP well.
Textures - model textures were pretty good. As were the armor texturing.
World Design - the world design was good, from what I experienced. I didn't get stuck anywhere I couldn't get out of and, believe me, I tried. The world also flows well into each area and the quests sort of push you in the necessary direction. You won't get lost or not know where to go with the way this game is designed.
Instance RVR - very neat. I like how they introduce this really early. I'm not sure if there are any balance issues or not, but the one shot I gave this Destruction (my side) absolutely creamed the Order side. I looked at the results and I was sitting pretty with 28 kills while the other side's best had just over 10. Most of my side had over 20.
Classes - I like how some of the class mechanics vary. A Black Orc plays differently from a Chosen but I did get the impression there were other classes which paired off easily.
Grouping - The Holy Trinity of a group is not required and getting into a group or adding people to a group is quite easy. I liked being able to do the Empire PQ with just me (a Battle Priest) and three Bright Wizards (it was hectic for healing but fun!).
Combat - solo combat had about the right pace, though grouping seemed to make things go faster. Champion level creatures were a good pace for killing.
Models - a couple of the models with cloth had clipping and overlapping issues. I believe long hair also was an issue.
Character Variance - it wasn't easy to tell one character from another. A big part of this is due to lack of customization in the character creation. The other part that really doesn't help is gear. It seems the gear upgrades are less obvious. The initial jump has something, but after that, it seems most armor in that 'tier' looks the same. *I'd be forgiving about this since it means less work for player PCs to render so it suits the PVP/RVR/PQs for performance. Dye seems to be one way of separating your character, but most of the colors aren't all that impressive and they seem to have the same availability for each race. I strongly suggest they create color palettes for each race with some of the overlapping ones being the more expensive (hey, make people pay to conform to guild colors). Costs are also tiered so certain colors are more expensive - I get this concept, but I don't like it, especially when you're already so limited.
Performance - bad. I'm pretty disappointed with the performance of the game given the system I have. It is more than capable of running VG at the higher settings and EQ2 at the Extreme Quality setting. WoW... well, full blown. Some of this can be attributed to the large number of people on screen at most times - it's a zoo, really. I also noticed some degradation overtime so I suspect a resource leak somewhere. I also experienced a crash.
Bugs - there were a number of bugs. One involved the quest helper markers (icons over the NPCs heads) getting stuck in a mode which was annoying. Another had to do with a PQ in the Greenskin area where you're supposed to collect barrels - I picked up one and couldn't seem to pick up others. One involved creatures running away from you after you engage them then they come back - I don't know if it is intentional or not, but it was annoying because it's not like they were low on health or anything.
Textures - world textures seem a little weak. The ground and rocks seem a little bland in most of the areas I saw. Some were well suited to the area but others were just too common. Where are the shaders?
World Design - while a lot of people like that quests and the world ushers you into one direction while I like choice. Give me two or more paths to take. Heck, each class has three mastery paths, why not make quest lines for each one that emphasize that path?
Classes - I noticed the Disciple of Khaine and Battle Priest had identical gameplay which was somewhat disappointing. The Bright Wizard and Sorceress seem that way as well. I believe the Engineer and Magus are very similar as well. I think these are the only few pairings like that, but I'd have to see more.
Responsiveness - not so good. Somewhat understandable when over crowded, but when you're playing at 6am and there are very few people around, things (inventory, NPCs, abilities...) should react a little better.
PVE - there didn't seem to be a lot of PVE stuff early on. While that isn't entirely a true statement, that is a feeling you'll get because the PVE content you're doing is tied to some of the RVR elements you'll face. In other words, if you're an ork you'll be fighting a lot of dwarves and if you're a dwarf, you'll be fighting a lot of orks/goblins. It's almost like playing a FPS with computer controlled bots... same sort of gameplay, only it is easier because the bots aren't too bright.
In short, it is a decent game and I will end up playing it on release, though I suspect it won't hold my interesting for much more than a month or two. You never know, maybe the community ties will make it more enjoyable.
I have to agree with the nay-sayers in that it really isn't a "super-awesome, omg drop what you're playing now and play it instead" type game, but it is decent.