I would love to play with people who are "good" at D&D. A few years ago I was in a D&D 3.5 group with a guy named Brad Willer. He was very fun. He came to have a good time. He made jokes and laughed at other people's jokes. He smiled. When combat started, he would get into the action and dish out damage. He didn't know the rules so well that he could rules-lawyer it, but he knew the rules well enough to make an effective character. So, he contributed to the team.
He bathed. He was fit. He was normal and well-adjusted. He showed up on time. He had a good story to tell if there was down-time. He was relaxed and never got pissy if people did unexpected things (like talking about a TV show for 20 minutes). He tried not to metagame. He tried not to steal the spotlight or otherwise micro-manage other people's characters.
He never undermined/berated/argued with the DM, but if he felt the urge to second-guess the DM, he did it pretty damn nicely. He'd accept house rules, even temporary on-the-spot made up ones that conflicted with the books. When it was his turn, he knew what he was going to do -- nobody ever set a timer on him, which is way more than I can say for myself. I get timer'd a lot, as I hem & haw and try to figure out which of 30 spells I want to cast. But not him.
Lastly, he gave his characters personality. We never LARP'd, and even thought just speaking in character voices was weird. But even with those limitations, he managed to have a hilariously over-the-top warrior who was certifiably dangerous, arrogant, and endearing all at the same time. The other players rooted for him.
So, yeah. I think you can be good at D&D. I wish more people were. Hell, I wish I was as good as Brad.
Yep, you can be "good at D&D". Here are some ways:
-Recognizing when it's time to fight and when it's time to run
-Knowing what abilities monsters have and what "level" they are
-Knowing when to check for traps and disarm them
-Knowing how to check for traps and disarm them
-Mapping well
-Working as a team in combat
-Avoiding combat if possible (pre-3E)
-Knowing when the risk is worth the reward
-Being able to solve riddles and puzzles
-Building a powerful character (more for 3E and on)
-Knowing when to rest
-Knowing what spells to memorize and when to cast them
This.
Take it another way:
A guy playing a magic-user going on an adventure to slay the goblins of Bleak Hill who memorizes Magic Missile instead of Sleep...
A guy who draws the map and gets the party lost/going in circles because he gets his right and his left confused...
A guy who runs from a kobold while he's unhurt, but charges straight at a troll from which the rest of the party has decided to flee...
A guy who blurts out an obviously wrong answer to a riddle and gets one of the party death rayed as a result...
A guy who puts himself in bad tactical positions and the rest of the party gets beat up or killed trying to save him...
A guy who gets into pointless fights with wandering monsters that could have been avoided...
A guy who blunders into traps, ignores obvious clues, and needlessly angers powerful NPCs...
... is bad at D&D. And if you can be bad at something, you can be (at least relatively) good at it. You can at least be as "not bad" as possible!
Yes, you can definitely be good at D&D.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.