I suggest you try this website, it's called GamerDad, and it specializes in reviews for parents who wish to see what games would be good for their kids, and what games you might also enjoy.
http://gamerdad.com/
As for the Bionicle game, IGN just did a fairly explanatory review. The gist of it is that it's surprisingly good for such a franchise. Normally games based on non-game franchises don't turn out very well. Your son, assuming he likes Bionicles, would probably like it quite a lot. However, it is a First Person Shooter, so it might be a bit complex for a 6-year-old to hop into, but if he's played a lot of video games, then he'll probably do fine. After all, it is a children's game essentially.
http://ds.ign.com/articles/749/749876p1.html
Also, I might suggest this new game. Bomberman Land Touch.
http://ds.ign.com/articles/750/750220p1.html