I have been playing lots of the ET: QW Demo since it came out a couple of weeks back as ET is still one of my all-time favourite games. The good news is that many of the gameplay mechanics which are so important to ET and make it unique have trasitioned over well. The limbo menu, the classes, the choke points on the maps. All seems to be pretty much the same with some new very glossy paint. All that I love and so won't comment too much about it. The map included with the Demo - Valley is a very well thought - out and designed map although I'm not too sure I like the later 1/3 of it.. but getting there is awesome. My preferred class is engineer - and the main difference in QW is that they can now use deployables. So basically you can lay down (only in certian locations) either an anti-personel, anti-tank or anti-artillery turret to sit there and surpress the enemy. Against a very good team these become slightly less effective but I have seen many a tank and soldier being mown by my turret - they are simply the best static defenders.
The second big change is the inclusion of vehicles - both drivable and flyable. These work much the same as battlefield and similar games - some you can be the driver and the gunner and some you need a separate gunner. I found the GDF Helicopter/Gunship almost impossible to control - but i'm sure with some practice this would get a lot easier.
I still find the feild-ops class to be often a bit too powerful and if you have a few good field-ops on your team it makes a huge difference.
It seems the game has been geared toward a larger scale and outdoor envornments this time around as well.
I am looking forward to this weekend as I may be able to get my hands on a copy of the final game and give a full capeign a whizz.
These are my initial thoughts - can;t wait to get my hands on ET:QW now that I think about it..