@Khatharr: I don't think making a profit is bad! That's a pretty extreme statement for you to make.
(just kidding)
I'd just like to point out that there have been some games that are legitimately enjoyable (not warmed over shovelware) when played for free, and they offer only cosmetics as premium items. Some of them have found overwhelming financial success with this model, and I don't believe that they're behaving in a predatory manner, since there's no gameplay benefit to the purchase.
MapleStory and League of Legends are financially doing very well, as evidence for what you are saying.
"A new report from SuperData puts League of Legends' revenue for 2013 at $624 million." [1]
"In 2006, Wizet revealed they earned over US $300 million from MapleStory." [2]
League of Legends is estimated to be $964 million in 2014, and MapleStory is estimated to be $240 million in 2014. [3]
Mind you, these games are making huge amounts of money, every year. This is in contrast to games like Call of Duty, which make buckets of money once (the several months after release), and then they need to re-invest alot of money on the next game in the series.
I've played both Maple Story and League of Legends for a bit, haven't paid a cent to either, had access to all the same content even the paying users had, and enjoyed playing them. They were fun games. Not quite my cup of tea, so I didn't stick around, but they were very good games that weren't ripping off consumers.
I think one possible rule of thumb on the ethics question is, are you giving value to consumers in a fair trade, or are you tricking/getting/asking them to pay for things that don't actually hold up to the promise on the cover - in videogames, that promise is entertainment. If it's a trade of dollars for entertainment, are you holding up your side of the bargain, or are consumers left with buyers remorse, or worse, addictions to things they wouldn't actually want to be addicted to if asked straight up before they first played the game.
Part of game design includes designing to create an entertaining experience (though that 'entertainment' doesn't have to be enjoyable. It can be entertainingly aggravating, entertainly saddening, and so on), and so it is not unexpected the games can become addictive and are even designed in semi-addictive ways, like World of Warcraft. I don't consider World of Warcraft, as a whole, unethical. Even games like Portal 2 or Angry Birds can be partially addictive, because part of game design is releasing entertainment in response to input, in different loops.
The question of ethics in game design usually involves discussion about intrinsic vs extrinsic motivators (if someone doesn't know what that is, google it, there's been a good number of years of discussion about it now), but I don't believe extrinsic motivators are inherently unethical, and think they are a useful tool in game design.