Retoru said:
It's not legal to download a game, even if you own it. A lot of people like to throw around "fair use" and claim it's legal, but it's not. Under fair use you're permitted to make a copy of software you buy, but the caveat is that you have to make this copy.
Downloading a game, whether you own a copy of it or not, is not legal. You didn't dump it yourself, and in many cases it's been reverse engineered(also illegal) to either remove or crack the included DRM.
I'm not getting on anyone for piracy, I do it from time to time. But, I know full well what I'm doing isn't legal and I don't try to justify my illegal actions. To put it in simple terms, if you're caught downloading the best thing you can do is simply accept it and do your best to reach a settlement that you can manage. Trying to fight it will just rack up court costs and attorney's fees and there's no way you can win, the law was broken.
Do not underestimate the power of the Purchase Defense.
While downloading and installing a cracked copy of a game that you purchased at retail may be outside the letter of the law, I can't see any way of a publisher taking such a case all the way to a jury. A publisher would have to try to convince 9 out of 12 average schmoes that a customer who bought and paid for a retail copy of Bounceman 6, subsequently harmed them by downloading and installing a cracked copy from the intartubez instead of the copy on the disc that was bought and paid for, and that had money going back up the supply chain to the publisher's coffers. I rather suspect that the reason we haven't seen cases in the system that reflect these circumstances, is that when counsel has contacted suspected copyright trespassers, they backed down when presented with proof of purchase, and realized the impossibility of proving their case to a jury. And if they do want to take their case in front of a jury, well then they get to argue all about enforceability of EULAs (still a crapshoot, though the odds are against) and even better, the lack of software warranties in light of DRM schemes. I'm pretty sure no publisher wants to open that can of worms.
A secondary defense is license vs. ownership. As long as publishers keep insisting that customers are only purchasing licenses to games, and that you don't actually own the game that you bought on disc, well, then they'll be hard pressed to start drawing distinctions between the copy that was purchased vs. the copy that was downloaded. Of course, success on this defense comes at the price of bolstering case law for licensing vs. ownership.
Now, while you may be outside the letter of the law, morally you are mostly in the clear. A slight argument can be made that by downloading a cracked game off the internet, even if you've already purchased it, you're encouraging game crackers to crack games, though I'm pretty sure they weren't waiting for your endorsement of their practice. Now that's a vastly different situation than paying a cracker directly to crack your game, that then gets distributed, or paying money to access a private tracker, as those are more direct inducements, but even the former case may be allowed, as the DMCA offers a bypass exemption for compatibility purposes. But that wouldn't apply for most modern games.