tl;dr version, this game is great and you should buy it. The solo is fun, the storyline is pretty decent and the game has a charming sense of humour that should warm even the darkest of souls, which just happen to congregate on this forum.
Story: 7/10
Overall the story is good. I won't ruin anything, but there are a few plot twists here and there and a few scenes that might force a tear out of you if you're sensitive enough. There are quite a few funny moments, as well, Palutena isn't really the uptight bitch we thought she was, she actually has a sense of humour. There are a lot of cringe-worthy moments, however, and it never ceases to amaze me how the characters can go from mourning over the deaths of thousands to playfully joking in the span of about 5 seconds.
Gameplay: 9/10
Brilliant. Absolutely brilliant. This game is enjoyable in so many ways. Firstly and most importantly, the weapons system. There are 9 categories of weapons, each with their own advantages and disadvantages, and in each category there are ~12 different weapons to choose from, which are all unique in their own way. Not only that, but weapons come with different ranged and melee strengths and weapon bonuses as well. Ontop of that, you can have different power sets which do stuff in battle, so basically, the possibilities are endless. There is so much variety it will make your head spin and your genitals tingle.
Of course, you use these weapons to fight things. The battle system is fun, but the variety really makes it. Should i kill this enemy by bludgeoning it to death, shooting it to death, hurling a grenade at its face or by firing a massive *crag*-off laser at it? Decisions, decisions. But there are flaws, for example, some items are quite annoying. In particular there is an item that makes you auto-dodge attacks, and you will often auto-dodge an attack that wasn't even going to hit you in such a way that it actually hits you. Pisser.
Which brings me to the controls. Yes, they could have been a lot better, trying to move around while shooting and managing powers and stuff can be very frustrating, and they are the single thing stopping me from giving this game a 10/10. But really, you get used to them after about half an hour of playing. No matter how good you get, however, there is always a chance they will screw you over.
The multiplayer is also great, and fairly addictive. Light vs. Dark is probably the most popular game type, which is basically just a 3-on-3 TDM, but after a team dies a bunch one of their players becomes pit, a beefed up version of your typical soldier, and when he dies the team loses. If you hate working with people there's also free-for-all.
There are a few unnecessary additions to the game, I'm mainly referring to the option of offering up hearts (the game's currency, a bit sadistic I know) to the goddess. It does nothing but make the goddess walk up to you. I've looked it up, it has no other use. So basically if you want the goddess Palutena's tits in your face then spend all your hard-earned hearts doing this. Also *SPOILER ALERT* after a while you get a new goddess to offer up hearts too, which shares the likeness of ~10 year old girl. So if you're in to that sort of thing you can also lure the small girl towards you with your delicious hearts and get her tits in your face. Both me and the FBI advise against it. *END SPOILER ALERT*
Music: 9/10
They put a lot of effort into the music and it really paid off. There are lots of good songs, what more can i say? There is this dog that appears in the game for about 3 minutes, and they made such an awesome theme for it it's not even funny.
Graphics: 8/10
Obviously there are certain limitations in the 3DS' graphical capabilities, but they still manage to pull it off. The 3D isn't really worth using because of the whole eye cancer issue, but even without it you'll often find yourself just stopping and taking in the backgrounds of some of the chapters.
Overall: 9/10 Buy the game. Just *crag*ing do it.