I just started playing the game and I have to say I love Arena. I haven't bothered with the other game modes because from what I hear, they seem very conducive to angry players.
When I started playing, I hated neith, now I am trying to get neith first. Late game in Arena she kicks butt once you get your attack speed as high as possible.
ADDED 2: Nothing is worst in late endgame than a terrible Neith player, Neith can completely turn away a game in the hands of an average player. This only applies to lower levels since I am only at level 4, I don't know how good she is at higher levels.
ADDED 1: I might just buy all the gods, so I don't have to worry about grinding them out from now and in the future. Even if I don't play much, it seems like a good deal, to have so I can dabble in the game once in a while.