NMH1 vs NMH2.....they are very different, but very much the same. They fixed many things that needed to be fixed or expanded upon from the first one, but you loose some of the fun elements were in the first one too. Here are some examples....

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They used the same map between the two games, but how you navigate them are totally different.

The graphics in 2 are tremendously better, but you lose the ability to free roam in a miniature sandbox environment.

In NMH1 you can't free roam within the buildings/locations i.e. your home, the clothing store, the video store, and so on, but you could free roam the city.

In NMH2 you can free roam within the building/locations, but you can't free roam the city.

The side jobs (main money maker) in NMH1 are all mission based 3D encounters, NMH2 are all 2D classic-clone mini games. Personally I like the setup from NMH2 because the game is really a mix of old-skool AND new-skool styles of gameplay, I love it! :D

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Overall they are both GREAT games and should both be played by anyone who owns a Wii. They both have an extremely high replay value. :)