$20 could be spent in a lot worse ways...
Do you like those games in Highlites where you have to find all the hidden items in a picture. Did you ever watch "Finders Keepers" on Nickelodeon? Do you enjoy those bar games that make you find the differences between two pictures? Did you find Waldo?
If you answered yes to any of the previous questions, and have a DS and $20 then this game might be fore you.
Mystery Case Files : Millionheir, isn't going to change the way you look at your DS or revolutionize the game market, but its still fun. The "story" (if you can call it that) is that you are a detective and the millionare "Phil T. Rich" (no that's not a joke) has gone missing. It's up to you and your trust stylus to find him. I don't know exactly how you connect finding items on a screen to interviewing a suspect, but somehow that's the way to solve the case. Find enough items with in your (optional) time limit and then solve one more puzzel and move on to the next person.
There are around 10 different areas and their respective inhabitant to talk to and interview. Most of the time you are just finding the proverbal needle in a hay stack. Some of the other puzzles are spin offs of a jigsaw puzzle, bejewelled, and others. There are several special items and little gimmicks that the game uses well enough. Goggles see under whater, xray sees through things, and you can even blow in the DS mic to "clean things off".
Once you play thru the game you can go back an complete it at different skill levels, and as i said before you can turn on or off the optional time limit, making you work harder to find items. I would say that this game is great for travel but if that travel is on a bumpy road, prepare for motion sickness.
I rented this as a stop-gap game between several other big name titles that were coming out. It served it's purpose, and i enjoyed it. Like i said before if you have twenty bucks and just need something to do on your DS, you could do a LOT worse than this game.