Doing side-quests for cash is the only way to get some of the more powerful items, and to afford to upgrade your weapons.
You can ignore all of this, and, thankfully, the game doesn't punish you if you do. If all you want to do is concentrate on the main story and leave the NPCs to their own devices, that's up to you. There is no need to grind; NIER is perfectly beatable without it. And having the option is welcome: do you want a 20 hour Japanese adventure, or a 30 hour one? The choice is yours.
What's great about NIER is that, unlike so many JRPGs these days, you actually want to see it out to the end. NIER's ethereal, mysterious air, complemented beautifully by a quite stupendous soundtrack (the music that plays as you're out in the field digs a hole in your brain and buries itself alive) rekindles memories of Haruki Murakami's multi-layered dream-like worlds. Nothing is what it seems, says Square Enix's blurb, and truer words were never spoken.
Unfortunately, while NIER's nonsensical plot is adult and smartly woven, it can't help but succumb to quintessentially Japanese cheesy melodrama, particularly towards the end, and is just a bit too far out there to fully grasp. Really, only half of the story is ever properly explained. Throughout you know something isn't quite right, and you excitedly await huge revelations at the end, but satisfying exposition never comes. As NIER unravels the truth behind earth's shady past, there's more than a hint of frustration as the game does an Akira and decides making sense is for losers. Once finished, a new game plus option presents itself, and multiple playthroughs result in further story details, but why should we have to play through a game four times to get the whole story? The answer is: we shouldn't. I found more explanation from the list of must-avoid spoilers sent to us by Square Enix than I did from the game's dialogue and cut scenes.
Really though, compared with so many recent Square Enix games, NIER's story, and indeed its attitude to gameplay, is refreshing. It's packed to bursting with interesting ideas, from occasional 2.5D side-scrolling platforming to top down perspective puzzle solving. NIER's camera is in a constant state of flux, and only occasionally suffers from the embolisms that afflict so many third-person action games. One section, set in a horribly creepy manor, sets the camera in ceiling corners in classic Resident Evil style. As you explore its mysterious innards and meet Emil, a powerful young boy who eventually joins your eclectic party, you feel as if you're playing a completely different game. Later, there's a section with the camera set at a distant isometric view, a clear nod to old-school Western RPGs. At one point, the camera goes birds-eye, leaving you free to direct Dark Blasts with the right thumb stick in a section that brings to mind Geometry Wars. There's even one section which doesn't involve a camera at all, instead presenting the player with walls of "choose your own adventure" text. NIER, really, is one big electronic doffed cap to games past and present.
If NIER's genre-fusing gameplay is its strength, then perhaps it is also its weakness. As is the case with so many games that try their hand at being a Jack of all trades, NIER ends up being master of none. The combat, while functional, isn't brilliant. The graphics, while styled, are horrible. The 2.5D sections, while interesting, are throwaway. The text-based sections, while different, are completely unfair. In an effort to be as unique as possible, cavia has at points forgotten what it is that makes video gaming fun: fun. Some of the boss battles, while appropriately bonkers and screen-filling, are frustrating in the extreme, particularly when they go all "shmup" and spray hundreds of red blobs at you. And some of the side quests are so mundane that you wonder if they're designed to make you resent them.
Still, the wonderfully designed characters and intriguing plot do just enough to elevate NIER above much of what is coming out of Japan these days. It is, in many ways, the kind of game critics of the Japanese RPG have been calling for: different, fresh, and in parts distinctly un-JRPG. Not all of it works, but it's a commendable effort, and a memorable experience.