I'll start with the new features introduced besides the new UI. The most welcome new feature is Shared Media. Ho..ly... crap! A truly functional web browser on a prim. It's per face, per prim, can have several media elements, and puts parcel media to shame. Flash content works(though I've yet to test on something HTML5-friendly like Theora). I've used it to do a tweet completely within a prim that has Shared Media enabled on a face. So we can expect some pretty crazy media mashups from machinima makers and artists soon.
There are two new clothing pieces introduced in Viewer 2.0: tattoos and alphas. Tattoos are pretty self-explanatory. Alphas are basically the replacement for invisi-prims on avatars to hide body parts, used for non-human avatars like tinies and dragons.
Now I'll get right down to the new "web browser" UI design. While residents who have become very used to the old viewer's design will no doubt find the redesign frustrating at first, once you start to find where all the menus have moved to, you'll find that virtually no feature sets have been actually removed. Landmarks are still in your inventory(as some like Prok feared they would get replaced with a "bookmark"-like feature), the build tools are practically unchanged(with the exception of adding Shared Media settings to the Texture tab), and chatting/IM has gotten a bit easier to keep track of: profile pics are shown before each line of chat and when an avatar says multiple lines of chat in an IM before anyone else, those lines are grouped under that avatar's name automatically instead of having the name repeated every single line.
There's more stuff about the viewer that I like, but I'll defer that to this blog post from Second Tense, as it is covered in pretty good detail.
The Bad and The Ugly
I have to lump the two categories as one because quite frankly, I don't see any serious UI or feature issues that would put me off using Viewer 2.0 when it becomes the mainline official viewer. That being said, there is one major thing that needs to be addressed: it's seems
And while I said that virtually no feature sets have been removed, there does seem to be one thing missing, though I'm not going to crumple up in despair about it nor ignore it either(Well, it's still there although not as clean as in 1.23 according to Prok).
Also, it appears they are changing their open source release strategy by attempting to label Snowglobe 2.0 as the source code for Viewer 2.0 and onwards. That may particularly irk third-party viewer devs a bit, especially in light of the new third-party policies and registry launched alongside Viewer 2.0. I'm irked simply because there are no Linux binaries of Snowglobe 2.0 available yet(this has happened before, and I'm not gonna slog through trying to compile it). Also, Linden Lab needs to be reminded that when you release any GPLed viewer to the general public, you must provide the exact sources used to make it, not the sources to a distinct derivative, as Snowglobe is(unless it is the exact sources with just the name and logo different, then it's okay).
Viewer 2.0 is a big step forward, though there will be shock and adjustment pains. If you can get through the initial shock, then you'll find there's a lot of stuff in 2.0 you'll like.