Villains in fantasy gaming are often over the top, the BBEG, the boss monster. Step back from this and you can get a much more rewarding game playing experience.
In campaigns past I've gotten a lot of mileage out of one simple villainous feature- re-occurrence. For a villain to be really notable they have to be in play more then once. Players have to grow to hate them.
Black Pate an orc chieftain leading a modest sized tribe of raiding orcs. Black Pate wasn't tied to one dungeon and would sometimes hire his tribe out to other baddies as mercenaries. He was a cunning careful bully that cajoled his underlings and got them to take the blows and fled when needed. Stat wise he wasn't amazing being a pretty straightforward Orc chieftain as per the MM. He got his name form a noble woman's wig he had captured years earlier and liked to wear to make him highly noticeable (it also added a bit of memorable ick factor for the players). Eventually Black Pate met his end in battle against the PCs. The ick factor and his showing up for more then one fight made him a memorable villain.
Kleep was a goblin flunky of a more obvious BBEG (Kurg the Fearsome a Half-Ogre anti-paladin). He served as a combination lapdog, court lackey and jester for the great Kurg and when Kurg met his end Kleep was quick to praise his slayer as king. After a time it turned out Kleep was untrustworthy and dangerous, he managed to escape justice and turned up now and again in the service of an evil wizard or accompanying other balckhearts; kleep was last seen on a pirate ship the Pcs were fire-balling (mostly because Kleep was on it). Kleep was slightly exceptional having 5 or 6 levels of thief, he was still no match for a mid-level band of PCs.
Turning up again and again made Kleep a memorable villain.
Don't suicide your villains on direct attacks. Give time to display personality. Let them escape if they rightly can. Their recurrence will mean far more to your campaign then all the HP and speical powers ever will.