Well, that demo was awfully short. Considering I had to wait 3 hours for the download to then finish the actual demo in like 30 minutes...
Anyway, first impressions aren't completely bad, but it's just much too short to say much, imho.
Tutorial is completely scripted/layed out for you, but at least not very long.
The "real" mission (actually there are 2, you get to choose, nope it's one mission with different decals (chinese vs english text and rewards, completely identical map, though) lets you do what you want after the 2nd turn or so. It can get somewhat interesting when you face 2 aliens and have only one soldier in a bad position, but the aliens you meet there are relatively easy push-overs. Hopefully that changes later in the game.
The cover system isn't so bad, it makes sense to take cover in a game like this and it doesn't play too bad. You can't always reach a perfect position when advancing and a soldier caught out in the open might very well be a dead soldier (if more dangerous aliens will turn up - hopefully).
Graphics are ok, if entirely different in style form the old games. If the original borrowed heavy from 90s comic-book aesthetics, this one borrows from post-2000 action-flics.
Interface could use some tweaking. It's not completely unusable, but far from perfect. Choosing and then confirming an action like shooting should be much more convenient when using a mouse. Also I'm not sure if I can even shoot at random things (to e.g. destroy walls or cover) or only at enemies (edit: it seems I can with grenades, but not with weapons?).
Ultimately it depends a lot on how much scripting they will do in the missions (hard to judge as the demo consists of 50% tutorial) , how random they are/appear and of course, how the difficulty will be.
The relatively small teams might serve to give the missions more tension, but of course, if you used to play the originals with big teams (I didn't), you might be let down.
I'm also a bit torn about how you have to decide between missions, instead of possibly doing them all. Sure, you can't be everywhere at once, but surely earth has more than just 4 elite-soldiers ready? It mostly seems to serve as an excuse to limit the amount of rewards the player recieves through the missions, probably to enhance replayability. (edit: also probably to mask the fact that many missions might be identical)
If they really wanted to convince me of the game, the demo should have been much longer, though (and not just for the fucking huge download size). As it stands, I might as well have not played it.