I thought I'd give an update about Fallen Empire since I played it for a few hours last night. It definately feels like a tribes game, which isn't surprising considering its made by former dynamix employees (the people who made tribes 1 and 2), but they removed so many gameplay elements that it's a rather shallow game.
Some of the things it's missing are there are only 4 different weapons(chaingun, rocket launcher, grenade launcher, and sniper rifle), there are no varying classes of armor/speed, there are no packs (like the energy or repair packs), theres nothing to destroy or repair (no inventory, sensors, or turrents), there are no deployables (such as mines, beacons, turrets, etc), and there is no command screen.
It's still just a beta, so hopefully they're going to add a lot to it before it's officially released, and it is extremely impressive that the game runs completely from internet explorer, but unless a lot of gameplay elements are added, I don't think it will have any lasting appeal for me.