Simply halving HP's, which is essentially doing, doesn't necessarily make combats more exciting if that's what you're looking for, at best it just cuts the number of hits required to kill something.
If you want more drama then increasing damage is the way to go I think. Add 1/2 level damage to all critters and pc powers/attacks and see if that doesn't liven things up, get rid of some of the perceived grind and make things more gritty. It has a less noted effect of also increasing the value of things that increase your to-hit chance and reduces the value of stat bonuses to an attack making it less 'mandatory' to have high stats. (example: That +4 damage from a stat is matched at level 8 by the 1/2 level damage and surpassed at level 10).
This also increases the risk of fighting monsters above your level but that certainly makes things more exciting.
If you want more drama then increasing damage is the way to go I think. Add 1/2 level damage to all critters and pc powers/attacks and see if that doesn't liven things up, get rid of some of the perceived grind and make things more gritty. It has a less noted effect of also increasing the value of things that increase your to-hit chance and reduces the value of stat bonuses to an attack making it less 'mandatory' to have high stats. (example: That +4 damage from a stat is matched at level 8 by the 1/2 level damage and surpassed at level 10).
This also increases the risk of fighting monsters above your level but that certainly makes things more exciting.