Much better than Gamespot would have you believe.
Nier is a third-person RPG. It hasn't given into the recent fad of absurdly fast-paced games like Modern Warfare 2, that start and end in the same five hour time period. Contrary to what Gamespot would tell you, the pacing of the main quest is not bad. It stumbles at times but is overall what you would expect from a quality RPG. What Gamespot seems to tell you is that if a game is not paced like FF13, which is a lovely game but has none of the variety or open-world elements of a traditional RPG, it is not well paced. This is not a critical perspective.
From a critical perspective, Nier's side quests are built much like an MMO in WoW's vein, and should be ignored. This is Nier's largest failure, and the reason it doesn't deserve a 9 rating, but since side quests are in no way required for much of anything, they have not impacted my playthrough of the game.
Combat is easy but fun. You fight similar enemies throughout the game but the game likes to throw quite a few of them at you, and situations can become alarmingly difficult very quickly if you're not careful. Simply put, they'll whup your butt if you don't pay attention, so if you like fast-paced combat you're in luck. You get one of three types of weapons: One handed swords, which provide quick, weak strikes; two-handed swords, which you swing around slowly but are not half bad for crowd control, and spears, which are difficult to wield but powerful once you've got the hang of them. Some of the magic is a lot of fun, and a couple spells are useless, but the majority of them offer new and interesting play styles.
Nier gets a lot of attention for genre-meshing, but that's not really what it's doing. It's keeping you paying attention. It's hit or miss, and in general when they put you in a combat area with anything but a standard camera angle it's a miss, but it's also not a game killer, just a bad idea.
The storyline is standard anime fare, with a noble hero without a lot of personality but with loyalty and kindness to spare, and spare it he'll need to with a standard snarky book, tsundere-type tomboy (albiet with a much fouler mouth, as you'll see from the intro cutscene), and Shinji-esque child prodigy. However, the decision to cast him as a father, in his mid to late 40s, somehow lends humanity to the protagonist, turning him from a bland "I'll save everyone super double promise!" anime hero into a convincing father trying to do right by his sick daughter. It, as Gamespot has informed you, does not have the frenetic pace of a Call of Duty game, and that's just fine with me. If you ignore the side quests (and you should) there's very little padding in it, and it plays quite smoothly. There's some strong narrative ability lying hidden in this story, and while anime trope doesn't let you see it very often, in sequences like the Forest of Myth (you'll know it when you get to it) Nier's writing really shines.
I haven't seen anything wrong with the game's visuals. They don't wow me like FF13 wowed me, but visuals don't make or break a game, they just add to it.
The bottom line is, Nier is a fun ride. So long as you avoid the side quests you'll get your fair share of button-mashing combat that smells a little like Devil May Cry, interesting (sometimes annoying) puzzles, and superb, unique boss fights. (Definitely the highlight of the game.) You'll meet four fun characters, (I contend that Kaine is the best female protagonist in many years) hear some superb audio (top-notch all around), and stay on your toes for most of the game. If you're looking for a solid, 20-ish hour adventure game to play, Nier is worth a look.
[[Edit]]: After revisiting the game and playing through a new game+, I am bumping the score up to 8.5. During the second playthrough you get added content in the form of cutscenes, and you can understand the language of the Shades via Kaine. The added dialog as you play through the game, along with the second take on the ending, make Nier an emotionally powerful game that leave you second-guessing just about everything. The third and fourth endings, which I do not recommend shooting for (they require you to gather every weapon in the game, which is doable with a walkthrough but requires you to submit to the weakest part of the game--the sidequests--which may make you hate the game along the way) add another emotional layer to the game, and make Kaine an incredibly three-dimensional character. I would youtube them, there are some great caps already. A full playthrough of a NG+ takes all of about 3 hours if you skip the cutscenes you've seen already, so there's no reason not to do it.
Overall, if you have not played this game, play it. It is worth it. You could rent it if you're okay with marathoning the game (which is actually not bad, the game's main quest never really gets dull) but a buy will give you more time to enjoy the 20-30 hour main quest. $60 sounds a little steep, but compared to dropping $60 on "press forward for 50 hours," or one of those 5 hour FPS's that Gamespot seems to love so much, it's worth it.