The fighting system in D&D 4e is pretty darn fun all by itself. But there are extra bits you can add that make combat much better: Stunts (DMG p. 42), Skill Challenges, and Cool Terrain Things. Let's talk about these and other ways to make battlemat fights cool.
Talk through the battlemat setup
When you're drawing the encounter area on the battlemat (or laying out dungeon tiles) talk through the various interesting features with the players, and solicit ideas from them.
"These are fire braziers. You can kick them over to burn adjacent enemies or throw someone into the fire."
"This ruler is the ship's yardarm. If you're standing next to it, you can swing it around 90-degrees to attack everyone in its path (STR vs. Reflex, 1d8+3)."
"These vines grow across the ravine. With an Acrobatics roll (DC 15) you can grab on and swing from vine to vine at your Speed +1. You're balancing, so enemies have combat advantage against you, but you have the high ground while you're up there, so you get +2 to attack rolls. If you fail the check, you can still swing across at Speed -1 and you don't get the +2 attack bonus."
"Those cargo bails should be hanging in nets, and they can be cut open to send the cargo crashing down on someone."
Think about opportunities, not problems
Let's imagine a swaying rope bridge across a raging river. You might say that the bridge is precarious, so you have to make checks to keep your footing when you move across it, or you're slowed, or some other hardship. This is "realistic" but not very much fun. Instead think about the opportunities for cool stuff that the bridge provides.
Like, you get a +1 to Bull Rush attacks against people on the bridge and you have the option to push them over the side instead of just backwards. Maybe if you're at the middle of the bridge, you can deliberately shake it, making a STR vs. Reflex attack against everyone else on the bridge (and shifting them one square off the bridge if you hit). Now the bridge is a dangerous feature, but it's dangerous because of the opportunities it provides rather than hindrances that increase whiff.
Add Skill Challenges with tangible rewards
The PCs are fighting a faction of Night Goblins they haven't seen before, so you throw down a skill challenge. As a standard action, you can study an adjacent enemy (Insight, Perception, and Dungeoneering are prime skills). If the PCs can get 6 successes studying before they get 3 failures, they'll learn a weakness in the goblin's fighting style. When they fight these goblins again in the future, they'll get +2 to damage.
During a fight with an Ogre, the PCs can attempt a skill challenge to determine where the Ogre's hidden treasure cache is. He keeps nervously glancing in its direction (Perception), he might spill the beans if goaded with trickery (Bluff, Diplomacy), and he keeps a special key on his belt that disables the traps (Thievery).
Got any techniques to make D&D 4e fights cool? Share 'em!