Since UT2003 just somehow showed up on my desktop, I figured I'd give it a shot. Now to begin... EVERYONE BUY THIS GAME!
Now, for the in-depth analysis.
Weapons
Wow, they changed the weapons up a ton. Let's start with the translocator. Before, you had people who would run and use the tranny to dodge people shooting at them. Not no more. You now have a limit, 5 times you can throw it. After you throw it, your little meter fills, and once it's full, you get 1 more throw. So if you throw it 3 times, then when it refills you get 3, then 4, then 5. Get it? Looks extremely different too, hard to tell if you still have one shot somewhere or not.
The flak cannon is in some ways, better. It fires the little flak shells in more of a direct shot, and not so spread out. They also can only bounce once, which is probably good cause If I shoot from a closed area, I kill myself a lot
The rocket launcher looks sweet, but it doesn't seem to explode so much, and do nearly the damage. You also can only shoot 3 rockets at a time, and I tried second fire, and didn't get anything else. So I'm not sure if the rockets can bounce around now, or not. This is a very incomplete demo, so it might just not be added.
The sniper rifle, now replaced with the lightning gun, is decent, but I want my sniper rifle back. Now you have to wait 2 seconds for it to charge between shots, and of course, you shoot a huge beam on lightning and everyone can see where you shot at. Also, you don't seem to be able to kill in 1 shot. Personally, I want the sniper rifle back, but they thought was they wanted to get rid of it's strength in close-combat. The sniper-rifle is a long-range weapon, but as most UT players know, it's deadly at close range.
Levels
WOW! I can't believe how sweet these are. LavaGiant2 almost made my cry

The level has improved so much! It looks beautiful, but just the little things. It's not flat land anymore, it's supposed to be forced by lava, so it wouldn't be flat. But there's bumps almost everywhere, so people might try to aim their rocket at your feet and then hit the hill in front of you. For some reason, I just like the new look of it.
There's also tons of outdoor ones, and as bad as you may think they are by judging screenshots, they're actually a ton of fun. I was playing one where it almost looked like dinosaur bones on the ground, and a giant spine in the center. But the fog effects, and everything made it a lot of fun.
Double Domination
Ok, this is actually much better. The old domination, for those of you who didn't know, was like there's 3 points in the board. You run through it, and score a point. Then every 5 seconds you hold it (prevent the other team from touching it), you get another point. Now, your team needs to hold all the checkpoints for that amount of time before you get any points out of it.
Too Early To Judge
Those of you who listened to what Epic said about the leaked demo, it was real. This demo is very, very imcomplete. The AI for example, they suck ass. And it's not finished either. I was playing a deathmatch level and I had 2 people standing next to each other and they didn't do anything. The game ends after 1 point, and you never even get the point on the screen. It's too early to actually let you change your controls. You can't see stats mid-game, every single character skin is unavaliable. Hell, I never even got any CTF opponents until the bot on my team captured the flag, and then 3 of them joined.
Anyway, my aside from the parts that I can tell are unfinished, this game will kick ass! I am buying thios the day it comes out and probably won't stop playing it for about a year. GET THIS GAME... when it comes out that is.