Isn't this two suggestions lumped into one? Kind of hard to know what to vote when one likes one of the suggestions and dislikes the other.
Anyway, I kind of like the way that you don't know if something is hurt until you probe it, that would be ruined with a hp-bar. Spellcasters often don't see the monster they are casting spells on, so for them this wouldn't work, they would still need the messages to see if the spell has any effect and to see that long-lasting spells are still in progress (like ball lightning). But maybe the client doesn't have to show hit after hit on the same monster/kind of monster. Just update the text and flash it (first draw it in black and then fade it up to gray) ?
If a spell kills ten monsters, perhaps the text could say that instead of ten lines of "You killed zombie with burning hands". Ie:
"You killed zombie with burning hands" -> gets updated to:
"You killed two zombies with burning hands" and so on up to:
"You killed ten zombies with burning hands".
If two, three messages are repeated (ie You killed zombie, you killed skeleton, you killed zombie), I don't know if earlier lines should be updated in the same way or there should be many lines like today.
The order of events gets lost if one updates earlier lines and I don't know if/when that may be important. Perhaps the client could have an expanded view where the messages are kept without change, if/when one wants to know the exact order of messages (after a PK, perhaps?) ?
Anyway, I do like the idea of an visual effect on the monster when it is hit. In the simplest case, perhaps just flashing its color, until someone's made some better animations?