Every time I download and play through a new free MMORPG I usually spot a few similarities in that particular game that I've seen in other games, which is perfectly normal. I actually prefer that games borrow successful features from other games, but when a game looks almost identical to another game, there is definitely something wrong. MMO developers are definitely getting lazier and lazier and are simply looking to older games for inspiration rather than trying to be creative on their own.
The single best scenario of a game copying another is the case with MapleStory and Ghost Online. Before I explain the similarities, I'd rather show you a screenshot first.

Maple Story

Ghost Online

The games look almost identical, and they play almost identically as well. Ghost Online is a shameless knock off of MapleStory. Although difficult to see, the maps in both games are 100% identical. Players on the map for both games are marked by red rectangles. I'm not going to say that Ghost Online is a horrible game, as then I would be condemning MapleStory as a bad game, which it isn't. Both games are actually pretty fun to play, but MapleStory is hands down the superior game.

One company, TQ Digital, is notorious for their lack of creativity. Every single one of their games play just like every other game they have. Crazy Tao for example is a clone of EuDemons, but with cartoony graphics. And by clone, I do mean clone. Both games are 100% the same game, just with different graphics. Don't believe me? Please try it.

There are plenty of other games that are way too similar to other games; like Secret of the Solstice which copies Ragnarok Online and Combat Arms which is very similar to WolfTeam minus the wolves. I'm not saying these are all bad games, they're not, but Developers, please stop copying each other and work on new ideas.