This is a great game and i enjoyed playing it, but it was not extremely original and i didnt finish it. I found the upgrade system to be nothing special. Overall it was an ok game i guess.
Its no secret how to play the game, just keep moving forward at all times. It gets you more item boxes and allows you to pretty much ignore the harder-to-kill enimies. As for weapons i did pretty well with the heavy machine gun, the shotgun, and of course the melee (all fully upgraded dont waste your time with the middle upgrade). first thing i did was fully upgrade the light machine gun and then uprade the melee.