Cold is sort of a late bloomer. Once you get Benumbed and Sleet, and with good recharge, it will be a very good set.
The average -regen, -res and -def of Cold are higher than Trap and Dark. Although Poison Trap has a very high -regen but it’s duration is short and on a longer cool down. Similarly, Howling Twilight has same problem although with a high recharge, it will get better. That said, Heat Exhaustion appears to be able to sustain a even higher -regen uptime.
Even double Acid Mortar can’t compete with double Sleet because Mortar has a slightly lower base -res and -def.
One thing about Cold though is that you have to take all the powers which limits the build flexibility a bit.
It is best to pair with bots, thugs or beasts.