I chose Ninja as well and agree that right now, at level 40, it sucks unless you want to sneak by everything.
If I respecced and went with dual swords, maybe it would be good because you might actually be able to get some of the poison/paralysis buffs active on enemies, but with any other weapon it's near impossible.
I saw a video of a late-game ish (lvl 90) Ninja that was pretty beast, though. There is a Ninja Set later in the game that scales A with Ninjutsu and he was doing some heavy damage with a katana (about 1800 a hit I think). He would just run around unseen and back stab everyone insta-killing them. On boss fights he'd litter the ground with the caltrops impeding their movement and rip them up with his sword.