Like most things in life,DLC for gaming can be used in a good way or in a bad way.
First I'd like to talk about how DLC can be used in a bad way.
Having to use DLC to get a proper ending for Mass Effect 3.
Many people have put more than 100 hours of playing time into the Mass Effect series and a much loved feature of the Mass Effect series is how player choices carry over into the next game.Bioware said the decisions the player makes will have a big effect on the game's ending.
However,Mass Effect 3's character endings are all generic and they don't give the story closure and have plot holes and the narrative for the endings seems rushed.
Later on,Bioware released DLC to give the player a more meaningful ending for Mass Effect 3 but you have to download it and it's ending still lacked heart.
DLC giving you a competitive advantage online
In certain games(especially shooters)people who purchase DLC can use more advanced weapons that other players who don't purchase the DLC cannot.
Needing to purchase online pass code for prewowned or borrowed games.
Some Playstation 3 games require an online pass in order to play them and even though Playstation 3 games that require an online pass in order to be played online come with a free online pass,the pass can be only used for one acccount so if you buy a game that requires an online pass to play it online and the game is preowned or if you borrow that game from a friend and the previous owner/your friend has already used the online pass,you'll need to pay money to download a new code for an online pass(which is technically DLC).
Now,I'll talk about good DLC that's sold at a questionable price
Heavy Rain is one of the best games I've played from this generation and a prologue for it named Heavy Rain Chronicles Episode 1: The Taxidermist was released which focuses on one of it's characters named Madison Paige.EP1 The Taxidermist has creepy and very psychological thrilling moments just like in the main Heavy Rain game but it's extremely short(taking only 15 minutes to reach the end)and even though it has 5 endings you can see all the endings in 30 minutes and it was priced at 5$.
I like some of the DLC character costumes for Street Fighter 4 but I don't want to pay money for them.
Other ways DLC can be good but overpriced
DLC can add more game time to our favorite games or give us new weapons to use,new characters etc. to freshen up the gaming experience but often we have to pay for them and sometimes the new levels/missions are very short and often DLC is nearly the same price as a full game.For example,The DLC for Assassin's Creed 2 named Battle for Forli is very short(less than 1 hour) and cost me nearly 1/2 the price of what I paid for Assassin's Creed 2.
Good DLC that's free
Certain DLC for Skyrim can make it's graphics better and improve it's inventory system and give the player new spells etc.Skyrim's graphics are already nice to begin with but with a free patch you can make them even better.
More than 10 years ago when I played Need for Speed 3 on PC,I downloaded new cars for free and it added a bit more life to the game because I could try out the new cars.
Some patches for games can fix or reduce bugs and can be downloaded for free.
DLC that's good and worth the money
GTA IV's DLC named ''The Ballard of Gay Tony'' was priced at roughly 20$ at the time of it's release and can add more than 10 hours of gameplay and adds a nice nightlife atmosphere with nightclub themed minigames and a new interesting character/story elements.
How I think DLC should be used.
I purchased Street Fighter 4 not long after it was released,but afterwards Super Street Fighter 4 was released with new characters/environments.I think Capcom should have given people who purchased Street Fighter 4 the option to download the new Super Street Fighter 4 characters/environments for free because why should people who bought Street Fighter 4 not long after it was released and whom paid full price for Street Fighter 4 get the bad end of the deal?
If developers want us to pay money for DLC,they shouldn't make it over priced(such as charging 5$ for something you can complete in 30 minutes)and if they want us to pay money for it they should make it worth the money such as how The Ballard of Gay Tony is or was roughly 20$ when it was first released but it was more than 10 hours long and brought new interesting characters/storyline and new weapons,new missions and fun gameplay.If developers want to sell DLC that can be completed in 30 minutes they should charge 1$ but not 5$.
DLC can be good or bad depending on how it's used.Greedy developers might use it as a way to make easy money or it can make a gaming experience better but even good DLC can be overpriced but some good DLC is free or worth the money.