How to make combat more exciting?

[Lord Azagthoth]

In my campaign, in the very first fight, one of the heroes lost his left arm. These players are all used to D&D3.0 and 3.5 rules but did see the movies on which my campaign was based on.

They encountered two droidekas (the type of rolling tripod droids seen in Star Wars Episode I from which a Jedi Master and his Padawan flee from). The heroes in my campaign were just starting (some weren't even adult yet) but they came soon to know that combat could be deadly. From then on, they first decided, when they encoutnered an enemy, if they could reasonably win the combat without losses (if they recognize the type of opponents) and if not, what are the retreating options if it goes wrong.

During the campaigns, the heroes have grown and are able to grind themselves through mass numbers of opponents (as long as they don't something stupid or very heroic) but still have to rethink their option when they encounter tougher enemies. Even then, the danger of getting badly hurt, losing limbs (which can be replaced) is very real.