For what its worth Ive played roughly 20 characters into their 20s. Cold/Ice was about #17 to do so, and the first to hit 50. He was late to the game, but I couldnt put him down.
You are just fine solo. You get two single target blasts early, and a hold not longer after. By the 20s you have the sleet/ice storm combo which will nearly kill a full spawn of white minions (one blast each finishes the job, while you keep the liet held). You also have your third blast at 26 which will give you an excellent single target attack chain.
Arctic Fog is very nice defense, but nothing near Storms. You pretty much have to stick to whites/yellows when not grouped, which the storm doesnt have to do. Thats the only real negative I saw, but that gets remedied in the 40s with your ancillary pool picks.
And that my friend is cold/ice on its worst day. Put that very same Cold/Ice in a group with both shields (you can have a solo build with dual builds so you can use these slots for something else if you want. I never felt the need for two builds though) and your day just went from great to amazing. Once you have sleet going down on every group your teammates will be steamrolling missions. They have no fear with their excellent shields, all of their attacks do 30% more damage with a well placed sleet. You are mostly free to pick on the bosses once sleet is down, and AV fights are over much much more quickly.
Oh I forgot to mention heat Loss didnt I? You know how Nukes suck on defenders? What if told you, you could lay down a blaster damage nuke (Blizzard and Ice storm are not on the defender damage scale since they are pets), then toss down a heat Loss to bring your end bar back to full? It sounds pretty sweet, eh? Its a lot sweeter than you think. Especially when your team gets surprised by an ambush. Instead of dying, you just took out the whole spawn for them and you buffed their recovery and blue bar in the process.
You only buff once every 4 minutes, you are free to kill stuff in between thanks to a lack of heals. Its the only 50 I still regularly play. My friends always ask for him when we run TFs.
I am not biased at all, am I? You might want to take that into consideration