I can see that they've done away with the trinity inasmuch as there is no dedicated tank/healer/support mechanism - which is great because it doesn't force a group to wait for 30 minutes for a cleric or a tank to rock up and join the party.
On the other hand, from what I've seen in events so far, once you walk into dungeons there's going to have to be a ton of teamwork going on - at this point it seems that the Elementalist and Guardians have the best group healing abilities. So those aspects are still there, they're just not locked in stone.
I'm loving my Elementalist because I'm able to switch between pure DPS and Support as the situation demands - it's very similar to the way I played my Chanter in Aion, so it's not a huge jump for me. For those who are used to playing pure classes there may need to be some adaptation.
As Lycan said earlier - it's not all totally revolutionary although ANet did bring a lot of new things to the table. It's a breath of fresh air, which is something the MMO genre needs - although I'm starting to think GW2 might be my last MMO - as much as I enjoyed playing this weekend and as much as I look forward to what's coming I've reached the point where I'm starting to become a little jaded.
Or maybe I just need a break