If you enjoyed Prime 1, definitely play Prime 2. It's basically how Majora's Mask is to Ocarina of Time. Prime 2 does the Prime formula over again with a new world and an added mirror dark world akin to a Link to the past and a zillion other games. Level design is just as good as Prime and it's just a great game overall. Prime 3 is also good. It's a lot grander than the previous two, but can also be a bit more frustrating in that you often have some external force telling you where to go, which can kill the feeling of discovering places yourself. Still an awesome game though.