Wait..I forget (and don't have my books with me)..do temp HP stack? If not, then it's not so bad. If so, then barbarian + minions + great cleave = OH CRAP.
They do not stack.
Well, not really, because then you have the funkiness of getting a class feature at level 5 when no one else is getting a class feature.
The mechanic isn't the problem, the problem is that it's useless for four levels. Somehow solve that "uselessness" problem, and you've made me a happy camper.
The more I think about it, the more I think there should be a basic "rage" feature that isn't a daily attack. If you migrate the damage capacity from the abilities into this "rage" feature, the abilities don't look as sexy for multiclassing. Even if we get rid of Rage Strike entirely, the idea of moving the damage capacity from powers into a different feature is an important one.
While you get a class feature at 5, you are down one that you would otherwise have until that level. Balances out in my mind. Perhaps I am in the minority, but I have no problem with rage strike not being usable until level 5. Doesn't bother me in the slightest, since its not something Id use every fight anyway. However, it does seem to go against their design philosophy yes, so how about some sort of non daily rage, sort of a baby rage if you will until you hit 5 and can use the big boy rages? I dont WANT to get rid of rage strike, I love the mechanic as is. Its a weapon you wont always use, but when you need to goto it its there to be taken advantage of. The problem is then to make it useable for levels 1-4.