Icestorm for defenders is very good. The thing about ice storm (and the nuke blizzard, too) is that they summon invisible pseudopets to do the damage since they have a duration. Well, when they ported ice blast from blasters to defenders, they didn't bother to make new pseudopets with lower damage - defenders get the *blaster* versions! This means that defenders using ice storm and blizzard get full blaster level damage out of them - which is very high damage for a defender. As well, as you noted, you have all of those tasty debuffs - after applying freezing rain, you will be doing *more* damage with ice storm and blizzard than a blaster would. Freezing rain (+ PBU if you have it) + aim + ice storm + blizzard = "OMGWTF how did that defender just do that?!?" It's great. 
Make sure to slot some accuracy in ice storm, though - despite what the 'real numbers' say, it only has standard accuracy. You can't see the 'miss' messages since it's a pseudopet, but the ticks can and will miss if you don't have any acc slotted. Freezing rain will somewhat mitigate this, but you can't always count on that. Aka, as usual, don't judge the power before it's slotted up - damage and recharge, too.
@MuonNeutrino
Student, Gamer, Altaholic, and future Astronomer.
This is what it means to be a tank!
Thanks for the response, mostly because I really wanted to take the power.
Also the accuracy discussions, not sure I would have picked up on that myself.
Now I just need to convince myself that aim really is neccesary... still not sure.
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One thing about aim which many don't realize is that the damage buff in the power is actually pretty good. The description makes it sound like it's got a 7% damage boost or something else similarly useless, but the damage boost is actually 50%. It's not just for hitting things, but for hitting things pretty *hard*. Ditto on power build up from power mastery, if you choose to take it - that one's got 80%, and lasts 12.5 seconds instead of 10, to boot. Not sure I'd take power mastery just for that one ability, as I personally feel that other epics may have more useful tools overall, but it's certainly an option.
Also, one other note - like ice storm, the 'real numbers' for blizzard's accuracy are misleading. It also has standard accuracy and needs acc slotted. Small price to pay in the long run, though!
@MuonNeutrino
Student, Gamer, Altaholic, and future Astronomer.
This is what it means to be a tank!
With Freezing Rain, your Aim, Ice Storm, Blizzard combo should hit HARDER than a blaster.
Triumphant Defenders Forever
Psylenz FF/Psi, ArticQuark Storm/Rad, Symon BarSisyphus Bots/psn, Max VanSydow Thugs/Dk, Cyclone Symon Bots/stm, Blue Loki Ice/Cd, Widow 46526
HelinCarnate:OMG it is so terrible. I have the option to take 3 more powers but no additional slots. Boo F'ing hoo.
Thanks for good responses. Guess this means that I have to try to find a way to fit in Aim. My problem might be that I want to many of the powers from the storm/ice pools. Then I wanted to take most of the powers from the elec epic pool.
Maybe you guys have suggestions on which powers I can most safely skip from these 3 pools.
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Elduris - very new to this game
Don't get thunderstrike, as its damage is rather poor. Then decide whether or not you really need another hold in shocking bolt. Charged armor is a must, and power sink is very good for a build like this that can potentially burn through lots of endurance.
Well, IMO you don't need three single target holds - two is enough. So you can leave out one of bitter freeze ray or shocking bolt, your choice. I'm not sure which one I would keep, myself - shocking bolt is a better hold, but BFR comes somewhat earlier in your build. Ditto, thunderstrike isn't *that* good - it's fun, sure, but not a must-have. From the storm/ice part, you don't have anything to stack thunderclap with, so it could also be skipped (though the FX and sound *are* really pretty on that power). You also probably don't need both gale and O2 - whichever you took for default, I wouldn't really bother with the other one.
If you skipped bitter freeze ray, O2 or gale, and thunder clap, that's enough to fit in both a travel power and stamina before the 40s, and then you can take whatever epic powers you want from then on. I echo the recommendation of charged armor and power sink, and if you're skipping BFR then obviously take shocking bolt (2 holds = instaheld boss = good). For the last one, whatever strikes your fancy. The immob would normally be my recommendation for a stormy since it prevents knockback, allowing tornado to grind a boss into smithereens, but for an /ice freeze ray also prevents knockback and thus fulfills that purpose. You could take thunderstrike if you want a toy power, or one of the storm powers you skipped, or another pool power such as hasten or whatever.
@MuonNeutrino
Student, Gamer, Altaholic, and future Astronomer.
This is what it means to be a tank!
I was wondering if anyone had taken Icestorm for this build and liked it. Every guide for the ice blaster says that this power doesnt do much damage and much of this is because it makes the mobs run away way used.
For a defender this shouldnt be such a big problem because I have some crowd control in the form of Freezing rain available, so I was thinking Frezzing rain-Icestorm-Frost breath and see what comes out.
I would like to try this power but not if I have to immediately respect to get rid of it.
Has anyone tried this or have any thoughts?
Hope you can help.