I played the demo of this a few days ago, and it was pretty damn close to what I was hoping for – the gameplay has changed quite a bit – instead of action points to continually move, look, shoot, crouch, etc., you've essentially got the choice of moving twice, or moving and shooting – but they've modernized the game mechanics while still keeping a strong link to the original. I understand they had to refresh the game for commercial reasons; that's fine.
I do think the graphics are a bit out-dated, but since it's a strategy game, it doesn't matter so much. If this was an FPS, the game would be slammed for the graphics they've chosen to go with.
Firaxis know how to make strategy games, and their experience shows in the demo. As well as the fluid game mechanics in the missions, I really like the ‘beehive’ approach they took to base-building, and how research, promotions, etc. Are a bit more hands-on.
Long story short – while it's not going to top the original, and isn't going to be quite the same game – this is looking like the best ‘planetary defense’ game in a long, long time.
PS: for anyone missing the original, you can still buy it on Steam, and an indie company recently got Kickstarter funding to remake the original with nice graphics and an improved GUI – that'll be called ‘Xenonauts’. Apart from the graphics update, it's meant to be an exact copy, so you might be interested in that…