Not being a big 50 cent fan (pretty much not a fan at all) I didn't hold out much hope for this one. But it's actually surprisingly fun! Once you go into the options and set the music to instrumental that is!
Army of Two was a total let down and very slow where as this is pure mindless arcade action, smashing crates sends bling flying everywhere before being magnetically pulled towards your character (must be a rapper trick), scores flying up all over the place and you are able to string kills into combos similar to The Club.
The voice acting is terrible as is the plot but then again, it's no worse than say, Commando, which is an awesome, mindless, action film.
The achievements are easy enough to get and it's not too difficult playing through on hard first time, especially with a second person online (no spilt screen).
It's certainly not worth £40 but is a lot of fun with a friend or fellow G. So when the price drops (or you rent it) get out there and bust some caps!