The secret is, most FPS games are actually really generic, and Halo less so than most. How many straight FPS games (that is, not hybrids like Deus Ex) actually deliver as deep an experience as Halo? Half-Life is one, no question. System Shock 2 fits the bill from what I've heard, but that was out five years ago. More recently than that? Far Cry? Maybe, but that game is just as repetitive and definitely has fewer enemies than Halo. Doom 3? Yeah, right. Any of the Unreal games? None of them have a REAL campaign, except Unreal 2, and I hardly think that's the best candidate. Anything like Call of Duty or Medal of Honor? WW2 games are so different they can't even be compared, as they operate on wildly different mechanics. Anything I'm failing to mention is not deliberate, so please correct me. I don't want to claim Halo is unique, but I firmly believe it's not nearly as "generic" as everyone claims. It is DEFINITELY not the best there is, but when people start claiming they know of a "dozen" better comparable FPS games, I start to get suspicious. I mean, being the 13th best isn't actually all that bad, but I'm still not really convinced...
Criticising the "story" is ridiculous. What FPS has a good story? Half-Life? No, pretty much it has the same story as all the over FPS games. Aliens find a way through a portal, they attack. Halo's is no better, no worse. Aliens declare holy war on humans, you have to stop destruction of life. The story isn't the point, it's how it's told. Half-Life was almost superhumanly successful at telling its story; it still blows me away to this day. Halo is not quite such a brilliant storyteller but anyone who has completed the game will attest that they were very much drawn into the world and the events. You actually do get the feeling that you're waging a war against an alien race, and it's very convincing. Not to mention, no matter how you feel about the game's religious undertones and backstory lurking under the surface, it's there. It's not there at all in most FPS games.
"The same 3 enemies?" Unlike some of the level design, this is one area Halo pretty much shines in terms of quality over quantity. There are four main kinds of Covenant aliens, and each one must be dealt with in a different way. Unlike almost any other FPS game, you actually have to manage your weapons. This is actually important, since again unlike most FPS games you can only carry two. For example, jackals have shields that cannot be penetrated with projectile based weapons. If that's what you have you have to sneak around them and get them behind their shield. Or you take our their shield with energy weapons. Other enemies have actual body shields like Master Chief, rather than a physical shield they hold. Just within those four Covenent enemies, there are a huge amount of tactics that must be exercised. To quickly recycle enemies and bring in new ones would absolutely make the game less rewarding, since by the time you get good it's a great feeling to be able to actually dispatch each of those guys in your own personal way, since you've been learning to deal with it the whole time. And then on top of that there are the Flood, who have a bunch of different enemies, and that's not even taking into account all the different kind of Covenant vehicles and turrets which you have to deal with when you're outside. Anyway, let's be honest, here. Why would an alien force have a myriad different "types" of enemies? Where would these types come from? Again, this just makes the war all the more convincing, since you feel like you're fighting a cohesive force rather than some bizarre hodgepodge of almost randomly-generated demons or monsters. And in most games that do have such wacky forces, it's spoiled by having the enemies pretty much all take damage the same way. Sure, it's sometimes better to use a certain gun, but it's much less tactical. In Halo, every single gun in the game (including the "shitty" plasma pistol and the needler) is almost necessary at certain points throughout. You'll never stop needing them if you're really trying to play the game. The game's design is extraordinarily solid.
And speaking of weapons, "unoriginal weapons"?! How do you figure this?? I mean, it has a pistol and an asssault rifle and a rocket launcher, sure, but how many FPS games don't?? Plasma pistol with its charge-up shield-removal technique (a crucial part of taking out Elites) and rapid-fire technique (which can basically slow enemies to a crawl if you're fast enough with the trigger); needler which shoots tiny little combustive tracking explosives; ability to melee with any weapon, a crucial ability rather than a last resort, and every gun melees differently... Etc. How many games actually have a whole set of original weapons, and why would you even need that? When the weapons are as balanced, nuanced, and across-the-board useful as Halo's, how much more outrageous do they need to be?
Levels repetitive? Yes, and it's really frustrating. It's too bad that Bungie was rushed, but believe it or not the game is not actually unplayable. The gameplay is so ridiculously balanced and solid that it's not nearly as painful as it would be in a game where you simply run around with the same most-powerful-gun blasting everything. It's still annoying, but it doesn't make the game bad. If it's too much for you to deal with, then play it on cooperative mode and suddenly it's a lot more fun to be churning through these levels with a friend (speaking of features other FPS games don't have these days...). If it's still not fun enough or if you don't have any FPSing friends, then try out the multiplayer, which is still better than most of what's out there. Everything I said about weapon management is just as true in multiplayer, perhaps moreso because your opponents are doing it too. Add to that the gajillion built-in gametypes, almost all of which are a blast, and you have ludicrous replay value. By the way, for those ragging on the single-player compaign, don't forget that the thing that keeps most of us coming back to the game is its multiplayer, which still holds up. If you STILL don't enjoy it, Halo is not for you, too bad, but like it or not, it is not a bad or mediocre game. I don't really enjoy Counter-Strike (for example) much at all but I don't mind at all saying that it's a great game. I completely understand why so many people think it's excellent and play it so much, it's just not for me. Nothing wrong with that, I think.
I think a lot of the people who really don't like Halo are PC gamers who honestly haven't given it the time and effort it deserves to see how deep and complete a game it is. I can relate because I was once one of those gamers (I've only really started playing console games in the last few years). It was only due to the persistence of my Halo-playing friends that I played the game enough to realize how brilliantly-designed it is (and that's one thing that even many "good" FPS games are occasionally not).
I don't know why I'm going to so out of my way to defend Halo, since it doesn't really need to be defended. I'd do it for any game I think is this great, though, no matter how succesful it is.
EDIT: Don't forget the rechargable shield. That sounds lame, but it adds a LOT to the gameplay, especially in multiplayer.
