Arwen is definitely interesting.
Not much reason to play Gandalf vs. other options.
Boromir is the jack-of-all-keywords with no real game text. Could be played with
Smeagol BoGS and RB Rangers.
Eomer has the cheap twilight cost, but not much advantage. Damage +1 isn't a big deal when with his spear and
Firefoot he'd be essentially dmg+3. I'd go with one of the other Eomers anyway.
I don't really see any balance issues.