Not at all! As much as Dead Space encourages experimentation, it also urges familiarization. You can unlock an achievement by only using the Plasma Cutter in the game, and while you will find certain situations in which Weapon A works better than Weapon B, you're not required to catch them all. If you find the schematic for a new weapon, purchase it, and then decide it's not for you, you can always sell it back for half the credits at one of the Stores and invest the credits in resources or Power Nodes instead. I dumped my Flamer and Pulse Rifle during my playthrough; other plays might not. It's up to you. Isaac Clarke is a silent protagonist, and while Visceral Games did a great job of giving him a personality despite it, they also left a lot up to the player. He never has a moment where he says, "I love the Contact Gun!" so you're not breaking the series cannon if you elect not to use it.