I like the idea of DLC and they have definitely made it more accessible. Maybe it's because I can't wait for DA:O =P
I think most of these changes are caused by higher production costs and the competition between purchasing new and old games. DLC potentially allows you to enjoy games you like for longer, instead of trading it in right away to get the next big game (which is something I did for a while)
Co-op and online just adds to replayability. And as the market expands the people who get into gaming are more interested in the social side of playing the game instead of the game instead of a single person story line.
Both of those are great for the industry.
For me the worst thing has been hype surrounding games.