First, Lego Star Wars. I've played this on three systems, Wii, X Box 360 and PSP. I've seen the DS version played by my nephew. The best part of the game is the sheer length of time it takes to play through the entire thing. It lasts weeks and weeks, if you are playing it regularly, but not constantly. It is a cooperative 2 player, which I always love, and a very enjoyable one player.
I was asked particularly about the rating of E-10 for comic mischief. Let me explain that, Legos die. You blast Lego Storm Troopers and other Lego "bad guys" (and Jar Jar). That is the reason for the rating. That said, if your children have seen the Star Wars movies, they have been exposed to more violence. The violence is a bit funny, in all honesty, because the characters break like Legos break, into pieces. There is no blood or guts and the violence is confined to fighting. Use your judgement in letting younger kids play this, the rating is a suggestion. Most families I know have let this game be played my younger children (6+, usually).
The actual game is really fun. You journey through all 6 of the Star Wars films, which are broken up into 6 sections. First you play through in Story mode, and have to play each film in order, but once you have completed an episode in Story mode, it is open for Free play. There is a nice combination of "ship" levels and character levels. The game can get complicated at times, but it is easy to play once you get the hang of the buttons.
As for how it plays on each system, PSP and X Box play very similarly, you mash buttons. One the Wii you have the option of swinging the wiimote or button mashing, depending on how you want to play. DS, lots of tapping, loud tapping. Other than play, the key difference between the systems is that on X Box 360 you can earn achievements. They are pretty funny too, there is one for killing Jar Jar 20 times. Needless to say, it did not take long to earn that one.
Overall, Lego Star Wars is a nice family friendly game. I enjoy playing it with my 7 year old son, it is easy enough for him and entertaining enough for me. As for the rating, each parent knows their child and what they can handle. Just another note, it is easy enough to find the Star Wars games (there are technically 3, even though the complete saga is 1 and 2 put together on one disk) used. That helps save a bit of money.