DownLoadable Content has been hailed by many as the saviour of gaming. There is not a game journalist out there who doesn't fawn and prostrate over the concept. However, I believe it largely to be anti-consumerist and actually detrimental to decent game production. I'll address some of those points here:
Product Functionality. Do you remember the old Commodore 64? I do. I remember the cassettes, the half an hour to load, above all I remember the fun. I also remember that the game HAD to be completed before it went on sale. This set the bar at the correct height because developers ensured that EVERYTHING worked as it should BEFORE the game's release. Unfortunately, the same medium used for DLC is used to patch games that lazy developers haven't properly tested prior to release. There is now no incentive to release a fully functional game because "Hey, I can patch it later". It also seems to end up with us being beta testers with some of the poorer efforts that need continual updates until they function correctly. Just code it properly in the first place, put some effort in prior to release and (by no longer having a crutch to rely on) you'll end up being a better developer with better games.
Incomplete Games. There have been numerous instances where developers actually had a complete game to release, but deliberately held back certain maps and levels so that they could nickel and dime us by charging for it later as DLC. What it effectively means is that content that would have previously been included in the game is now being supplied as additional add-ons and we're being charged for it, which means we're not getting value for money with our original purchase. This is money pinching at it's worst and shows that developers can be greedy as well as lazy. Very poor IMHO.
Exclusivity. By restricting DLC to certain retail outlets, what you end up doing is giving the retailer license to charge more for what is essentially the same game. This is against the spirit of free market competition and results in ridiculously high prices which effectively works against the consumer, not for us.
2nd Hand Value. This effectively goes down because DLC (for instance, some digital online passes that allow you to play multiplayer) will no longer work on 2nd hand games (which won't come with an unused pass). Which means your product (which you have the RIGHT to sell on) is deliberately having it's value reduced by the developer. I'm not sure why developers are so hell bent on destroying the second hand market, apart from the fact that they're greedy. It's similar to buying a £20,000 car, aiming to sell it on for £10,000 after 3 years and then being told by the car manufacturer that they're going to deliberately try and reduce it's value to £5000 for you. This is why the gaming industry is in trouble, developers are getting greedier at the expense of us consumers.
Pay To Win. This is what developers are turning the gaming industry into. Want to complete the game in good time? Pay for this item via DLC. Want a better vehicle? Pay for this item via DLC. DLC used in this way simply allows developers to end up with more money than they could have had, had they made the game complete in the first place. You can tell this DLC apart as it usually releases very soon after the game itself has launched in order to maximise profit for the company. Fine from a business sense, bad for consumers.
Loot Boxes. Alternatively called Loot Crates, Loot Drops or Prize Crates, this is similar to the above but deserves it's own subheading. You basically pay money to access the contents of a box, which then digitally downloads to your game. The problem is that many of these are random and pot luck as to what you get. This puts this into the category of gambling. In games for children! This is a disgusting practise and proves that many game developers and companies have little to no morals either.
Developing New Content. This is the only instance where I agree wholeheartedly with DLC. This DLC normally releases a long time after the initial game, because the developers have had to have time to work on it and haven't "pre-planned" trying to squeeze more money out of you instead. It allows genuinely NEW content to be released, piecemeal, and you can choose whether or not to buy it or not. Some DLC ends up being excellent value for money (multiple new modes, tracks, maps, weapons etc etc) and others tend to fall short so you can vote with your wallet and decide to buy it or not. It can add longevity to a game you have since completed or, in some instances, functionality as well (e.g. the speed run tests in GT5). Overall, I like DLC that's well done like this.
As you can see, that's six negatives and only one positive. I think it's safe to say the cons far outweigh the pros and DLC only demonstrates that developers are increasingly being lazy and contemptuous of customers. It is also the biggest reason the gaming market is shrinking - they have to learn that most of us consumers can see through their motives and are less and less impressed as time goes on.