I'm not entirely sure, since I have yet to play Investigations, yet, but I'm thinking that if you want to get the most out of Edgeworth's character, you should know about his history. Still, most of the games are pretty easy to pick and play, knowing nothing of what came before. My first AA was the third one, after all, but it was so good I went and played the first two. I would recommend going ahead and picking them up for the DS, or purchasing the Wiiware versions if you own a Wii. The games are great, I'm sure you will enjoy all all of them. PS: Parts of Investigations take place around the same time as Trials and Tribulations, so I guess you should at least play that one (And it's my personal favorite, too, as you may be able to guess from my avatar).