While I am not a beta tester, I have been following TOR very closing for the last couple years as I am very excited to play it. This is what I have gathered from all my researching.
Characters - There will be "paths" so to speak, similar to WoW's talent trees, but not exact, and I doubt there will be much difference in one Sith Lord and another.
Combat will be like standard MMO's, not quite like DDO, less twitch, and more hotkey/rotation style play.
End Game will include some raids early, expect for this part to be like WoW/Everquest, starts out small, but each expansion will most likely add levels and mostly all high end content.
There will be lots of crafting, and I do mean lots. You will be able to make a lot of the gear you will use at any point in the game.
The leveling up process will be close to Knights of the Old Republic, with cutscenes, a story arc that lasts most of the way up. There will be dungeons and such as well, which are more optional than anything.
PvP will be a big deal, and include War Zones, ala Battlegrounds from WoW.
Thats all I can remember at the moment, but I am excited about it and will be there to try it out probably at launch or shortly after.
Does this mean I am leaving DDO? Heck no, I don't think one will replace the other.
I am thinking TOR will be more RPG and PVP like, where DDO is more custimzation and better raiding/grouping and so forth.
I will say there are going to be some similarities with WoW, of course, Bio - Ware isn't dumb, and WoW does have a HUGE playerbase. But Bioware does have some quality games.