I got to sit down and play the demo for about an hour today, and my initial impression is: meh. Don't get me wrong, I've been kinda pumped about this game for a while, but I just didn't get into it from the demo. Here's what I feel about it from my (admittedly short) time playing it...note that I could be slightly biased, given my background (also expect lots of Saints Row comparisons).
Pros:
Sense of freedom. Jumping is fun, just like we all thought it would be. There were a number of times that I would see an agility orb way up on top of something and think "man, how can I get that?" and then found a way to do it. Driving is...ok, but I found myself on foot more often than not.
Framerate. I did not once notice any kind of hitch (even minor) in the framerate. I wasn't using crazy explosives or anything like that, but I was still very impressed in how they kept that FPS up.
Co-op in the demo. Didn't try it, but the option was there.
Mixed:
Trigger-based driving. Driving is something that I was really torn about, but I love driving with the triggers on the 360 gamepad, and I was glad to see that in this game. However, I was also pissed off at it, which I'll talk about in depth below.
Physics. Also something I had mixed feelings about. It was cool to have the super strength and such, but it seems like the physics were still missing something...they're not as "out there" as Saints Row (especially the ragdolls, which is where my major beef is...I like ragdolling a LOT), and it just felt muted as a result, which was especially noticable against the rest of the exaggerations in the game.
Aiming system. You can aim your gun like in Saints Row, or you can hold LT and lock on. When locked on, you can use RS to select which part of the body you want to aim for (head, chest, right arm, left arm, legs). In theory, this works really good, but in practice...it felt really awkward. Maybe it's because I'm not used to it, and I was getting better at it by the end, but all I was doing for the most part was locking at close range and shooting people in the chest with a shotgun...any time I tried to do anything more complicated, I died.
Demo limitations. I know why they're there, and they really are pretty lax (1 hr. time limit, one whole island (out of 3) to explore), but I really can't say this is a pro. Could have been much worse.
Cons:
Driving. Driving in this game feels really cheesy. Brakes don't feel responsive, steering doesn't respond all that great, car physics feel really...off. And not in a good way. I did not like driving in Crackdown, not the agency vehicles or the cars off the street (of which there did not seem to be many variants).
Inability to shoot and drive at the same time. You can't do it. After SR did it so well (in my opinion), there's really no excuse for this.
Lack of activities. You can shoot gang members, you can race, and you can jump around. That seems to be about it.
Music. There seems to be only a few songs in the demo, and they're not terrible, but they're not good either. I couldn't find a way to switch radio stations or anything like that either. This is minor, as I can play other music on my 360 at home, but was very frustrating on the kit I was playing on.
Close range combat. Oh god is this terrible. When you get right up close to someone, your RT (WHICH IS SHOOT EVERYWHERE ELSE) becomes punch. And punch is pretty weak. It's pretty easy to get into punch range too...even when I was avoiding it, it would end up happening, and would piss me off every time. Also, every time this happened, my view would get screwed up somehow, and I'd be looking the opposite direction staring at the ground.
Story? I didn't see any. "Go assassinate this dude. He's bad, we promise." "Get this supply depot so you can respawn somewhere else." That's about it.
Aliasing. First thing I noticed was how bad the aliasing was in the garage you start out in. Ask Feenix, I was bitching about it on AIM. Though, it didn't look as bad in the screenshot I took, so it may have been my display.
Lack of customization. Sure you get to pick from 8 burly dudes, but I want to customize my character in every way possible. I picked the Russion guy, who is pretty BA, though.
Flashiness. Maybe it's just me, but there is way too much neon in...whatever city Crackdown takes place in. Driving through the one race mission I did almost gave me seizures.
In the end, it seems like it could be a fun game, but at this point it's looking more and more like a rental for me. I'm interested to hear other goon opinions when you get the chance to play it, though, and I'll probably play it a few more times next week to see if my own opinion changes. I know it looks from the lists above that the cons greatly outweigh the pros, but it was fun, it just seems to have a lot of faults as well.