Just wait 'till you get fearsome stare 
In other words: Yes, it'll get better.
/dark is quite unusual in that you get some of the fundementals of the set early (twilight grasp, darkest night and tar patch) early but along the way you continue to get lots of useful tools. Fearsome stare is a massive fear cone which locks down the mobs once you have herded them onto tar patch and debuffs them even further. Petrifying gaze is a pretty decent single target hold for dealing with the kind of mobs who you don't want to shoot back 
, beware though that it has a flight time and only holds once the target has been hit. Black hole is potentially useful (mob intangibility) but is the power more often than not dropped from builds as intangible enemies are not universally popular with teammates. Dark Servant is supposed to be very good (only just got fluffy so learning where best to use it) as it has an evil debuff aura around itself and can spam heals, immobilises and debuffs a-plenty. So all in all, a very good bag of tricks.
@Moondog
Union:
CoH: Moondog (WS); V-Rock (Tnk, semi-retired); Pole-Star (Bla); Demon Dog (Scr).
CoV: Midnight Gunner (Corr); Operative John Doe (Ban); Day-Star (Dom); Commissar Jaeger (MM).
Both Fire Blast and Dark Miasma are fantastic powersets with great powers all the way through. Your main problem will be trying to fit in everything that you want
oooohhh yes! iv just got mine to lvl 31 and 4 bars from inferno! hehe so much fun!!!!!
I rolled a fire/dark and am finding it great fun. Pull to corner with darkest night tar patch, rain of fire and fire ball and a dead mob.
Played other corrupters (dark/dark & AR/Traps) and never has this much fun as a low lvl. Only question is - does this build continue to improve or does it go down hill? Currently lvl 10.
Altitus doesnt have a cure just more alts