It's a fine game. just don't expect it to redefine a genre
I will start with all the good this game brings to the table. One of the drawing features of this game is the upgrade-able weapons which are all in there own way, pretty damn cool. a 44. magnum with trigger-able explosive rounds that when upgraded, become even more deadly the longer you wait to trigger is one of the greatest things in a shooter ever, and was pretty much all i would use in the game (not to say any of the other weapons weren't just as crazy). Another feature added on are perks, which were borrowed from COD but with tweaks and new ones added to make them slightly unique, and whats more, they're upgrade-able! One of my favorites is the leapers perk, which much like COD's abandoned drop a grenade after death perk, leaves a present for the enemy. Smart players could even use this perk to help seek out new enemies once they return. Finally, there's the killstreak rewards, lifted wholesale from COD again, but with slight tweaks, (and hey, at least you can say they beat them to the juggernaut armor, having whats called "mutation") all of these come together to make multi-player an altogether enjoyable package. The guns also help the otherwise avoidable single-player campaign considerably. One more thing i really appreciate about the multiplayer, and the game in general is that they gave some attention to detail as far as designing the maps, by which I mean the fact that you can actually shoot through tight spaces and things like the spaces between a pillar in a stair rail, which may go wholly unnoticed but add to the realism.
Now onto the bad of this game. First off, the bane of every shooting game from the last 5 years, the campaign. let me start of by saying that this games story mode isn't any worse than other shooters story, (Hell, its still less annoying than killzone 3) but that is not to be confused with praise. There isn't one likable character in the whole mode, from the wench wife who force f's her husband into throwing his ass on the line after having gone through all he did last game, to the one-note, melancholy, totally non-exciting protagonist formerly mentioned. Him and his goddamned glove will be the reason you skip most cut-scenes. While the gameplay isn't bad per se,(and can be pretty fun with 2 players) there are issues that show themselves as you go along in the game, like an enemy not spawning correctly, halting you in your tracks to look for him. AI will also cause a stop to the flow of the game by either not doing what hes supposed to or getting caught up on something. I wont complain about life not regenerating, because frankly it makes this game more exiting, having to find cover and watch your own back,(and if you have another player, this is pretty much a non-issue anyway) which is good because the level design sure isn't. It's a been there, done that affair, with everything reminding you of halo. (spoiler alert) Even the end of the game level, where you must destroy the "chimerian" AKA covenant ship, and the subsequent "last stand" moment where your hanging on by a rope, just feels derivative and makes you ready to just end it for the cheats(if your so inclined to play the game again) and MP skins. Its funny that for some reason when i beat the game i still didn't get the cheats, and while all i'd probably have to do is play the last section of the story again to get it, the risk/reward thought came to my head and i just said F it. Now as for multi-player issues, if you started playing anytime after maybe a week from launch, unless you have an extra controller and don't mind being kind of a cheater, you will have a verrrry frustrating time trying to play. everyone will murder your ass with there upgraded atomizers and quick firing mutators. And one gun i would have been completely content for them to leave out altogether is the auger. True it can only be used for a short time as a killstreak, but it unbalances gameplay so, that the team or person who gets it first is more than sure going to win. Hell, it be fine if all it did was shoot you through walls, but noooo, that son of a **** also spams walls of very hard to breach shields. Sure, you may think, but couldnt you just throw a grenade above the wall and trap them in their own protection? Well yeah, we've thought of that... but so have they. So you'll have this guy camped out inside a building with his perfect wall protection with a ceiling just short enough to defend from grenades, and by the time you figure it out, your dead. boom.
All in all, the game is a pretty damn fun shooter. in a class of its own, it stands well, and while it "steals" some of the great stuff it has from other games, the unique touches it has really make it shine. unfortunately because of those elements, it will be compared to games that are superior in the encompassing genre. While I cant quite call it an under appreciated gem, i can say that it is a hell of a fun distraction. Much like a rollercoaster ride, its fun while it lasts, but is a short lived thrill, and you may get sick of it fairly quickly