I always felt like having bullets being really fast projectiles (vs hitscan) feels more powerful somehow. A GDC talk by a Bungy employee on weapon balance talks about being able to see causality unfold over time being more convincing. Think there's something to that. Also, information captured in a still frame. Recently did some particle modding for Tremulous, clearly visualizing splash radius and adding trail effects to projectiles to show direction (even in a single frame) seem to be a Good Idea in general. Viewshake (subtle) and impact sounds are another two.
Quake could benefit a lot from all that stuff, imo, maybe need to look into the particle systems of some ports. Unfortunately the more traditional engines don't seem to have them. Tried DP particles a couple of times but that particle system really feels like an afterthought to me. FTE looks a bit more promising but haven't checked it.
About juicing-up presentation, really good presentation.
In the end it's all about applying basic animation principles
http://en.wikipedia.org/wiki/12_basic_principles_of_animation