Never worth it for one game.
Hell just rent a PS3 and MGS4 from a video store if that's all you are going to do.
You should look into Valkyria Chronicles though. It may interest you... it's got an anime like style and deals with military stuff (though granted no giant robots) like the anime in your avatar and sig.
http://vgchartz.com/forum/thread.php?start=150&id=26086
Official Valkyira thread
Also for robots. Sony is supposed to be getting it's own Super Robot Wars game. Which won't come to america but are REALLY easy to understand control wise... and a lot of the scneario stuff is easy to get on context.
I imagine it'll look like the 360 version. It might even have some of your favorite Anime in it.
If both of those games interest you as well... 3 games is a decent base to get the system and hope more games come out.
