I have a Ice Blast sentinel in the mid-20's. It gets played about every three months because it takes about that long for me to forget just how painful it is to play.
The problem is the attack cooldown and rotation. Ice Blast is painfully slow to use, you are constantly waiting for your attacks to be available again. (I do have Hasten but I don't have it tricked out with maximum recharge IOs)
The only way I can effectively level is to find a team to carry my frozen butt, solo play is very slow and painful.
If a future page can improve this recharge time for Sentinels, I'd be grateful. In the meantime...I'll stick to other sentinels I enjoy more.