Firstly, you can't say one game is better than another game you've never even played. That's just nonsensical, though the other game being Halo 4 and his persistence in trying to drive home the fact that Halo 4 is the better game despite never having played Destiny, should pretty much tell everyone what they need to know about his opinion.
Secondly, regarding the narrative, I actually think the story itself is ok. Decent premise, good lore, nice degree of intrigue and allure. The problem is with the delivery. It's ropey, disjointed and doesn't explain itself very clearly. You have to pay a great deal of attention to know what the hell is going on, as often important story titbits are thrown in at in-opportune times, not concise enough audio wise, or simply not fleshed out properly. But there's just enough there to keep things engaging and have me wanting to find out more.
About the mission structure, I agree it's pretty repetitive. But the mission structure being repetitive doesn't necessarily mean the gameplay is. In-fact, in some ways it's less repetitive than your average shooter (COD, Halo etc included), because not only do you get gameplay and encounters diversified by the vast range of different enemies, level and arena designs, weapons, stats, classes, powers, vehicles, co-op options, AI, random events and all the rest, but you also have the whole dynamic real time menu, upgrades, RPG esque progression, item and loot collecting, Tower hub and everything else, that breaks up the gunplay in more meaningful ways than in your average shooter, which usually just break away to a cut scene to switch up the momentum, pacing or level of engagement.