Night Beam’s purpose is to remove a card from your opponent’s backrow. Other cards with the same purpose include Cosmic Cyclone, Galaxy Cyclone, Wild Tornado, etc. all with their own pros and cons over Night Beam so choose the ones which works best for you.
Destroys your opponent's face-down Spell Cards / Destroys your opponent's face-down Trap Cards / Prevents activation of your opponent's Spell Cards / Prevents activation of your opponent's Trap Cards / Prevents responding to its activation
I've seen quite some Legend 3 HERO decks with Night Beam in them
There’s a work around it to bear in mind. The card being targeted can’t respond to night beam but if you’re opponent activated another card then the targeted card can activate in response to that instead.
Not exactly, Galaxy Cyclone's secondary effect when activated in the graveyard still makes it better since it removes face-up cards as well (still strong in the current meta against Vampires/Buster Blader/etc.)