So I nabbed that brand new Battlefield 2142 demo, a whopping 1.1gb, and overall, it seems to basically be a fancy upgrade of BF2. Which may or may not be a good thing depending on whether you liked that one. Gameplay-wise, you're still capturing points of the map, though it has a different effect on the gameplay now when you do so, by taking control of missile launchers which fire at your opponents' Titan carrier, a huge ship hovering above the battlefield. You have to protect this thing, even by going on board to defend it if its shield goes down. Or boarding the opponents if theirs does, unless you want to just wait till theirs explodes from rockets.
The downside I found was the same as in the last two Battlefield games; dying, a lot, and then running back to battle, a lot. You do much more running and walking than actually fighting. I still don't know many of the features and controls though. And if I played with just friends, it'd be ten times more fun, as are most of these sorts of games.
So, worth the download? I'd say yeah. The only other real downside was the fact that their login servers are dumb and told me my name was free, only to say the opposite when I tried to register it, so I had to use a different one. Finding a server without assholes and/or "cheaters" is the next step..!