I haven't played Oblivion yet.

Will we have:

Arenas where we fight against enemy 1-to-1
Get to choose a faction in the civil war
Get behind enemy lines by dressing like them
Dual-wield swords

You haven't read a scrap of news have you...

1. There is an arena in Oblivion where you can face NPCs 1Vs1 etc.
2. Don't think so
3. Don't think so
4. LOL....

We will have dual wielding swords yes. In oblivion we had an arena so they're might be one, and I don't know about the other two yet haha.

There is an arena? Can anyone else confirm this? link? Ive seen nothing on the arena so far.

I'm rather hoping that with a civil war in Skyrim it will be possible to choose sides. At the very least it would create a consequence for helping one group by the other disliking you. I also wouldn't be surprised to have faction armor and disguises. It first made an appearance in SI, then was used in FO3 (I think) and F:NV. I'd expect to see it again in Skyrim.