The boss battles in Deus Ex: Human Revolution suck. Hard. The people of the Internet appear to agree on this notion. While they aren't game-breakers, they are clumsy and uninspired bullet sponges whose design runs counter to the nature of the rest of the game, which should not come as a surprise given that the bosses' development was outsourced by Eidos Montreal to a different company. You see, Revolution is all about the ability to deal with situations in multiple different ways, and while the game is fairly slanted towards stealth play, there are varied and intricate ways through most events. In fact, there's a good argument to be made that the game should have let me somehow sneak or talk my way out of the fights altogether. However, with the bosses in Revolution the only real choice is to figure out what weapon is the best for exploiting their horrendously simple attack patterns.
The saddest part of these bosses is not that they're bad, but that they could have been extraordinary if they had gotten some more specific attention. Revolution is often described as a wondrous offspring of Metal Gear Solid and Mass Effect, and by "often described" I mean "described by me". However, the unfortunate part is that Revolution seems to have taken more after Mass Effect in regards to bosses rather than Metal Gear, which is a damn shame since the Metal Gear series has given us some fantastic bosses over the years.
WARNING: Minor Spoilers
In fact, during three of the four Revolution bosses I could see clear, unrealized similarities between them and some Metal Gear bosses. While taking after some existing fights might not be particularly original (or…original at all), it would have been far better than what was actually produced. And remember, Revolution isn't particularly innovative to begin with. It just successfully meshes several existing mechanics into one game. So importing some bosses along with everything else would not have been any sort of mortal sin.
The first boss, Barret, is a big, hulking brute with a giant gun that shreds anything in it's path. Of course, Metal Gear has an easy contrast in Vulcan Raven. Like Barret, Raven requires the player facing a much stronger enemy, albeit a much slower one. The usage of cover, hit and run attacks, and knowledge of the chamber are crucial to avoid getting cornered or caught out in the open. The player has to be sneaky and time his movements accordingly, which fits in perfectly with the overall theme of the game. Sadly, Barret's battle does not utilize these mechanics at all, which is a flat-out bizarre development since the rest of the game is pretty much centered on them.
The boss AI in Revolution is so simple and easy to fool that all of the fights are total jokes. For example, while Barret always knows where the player is regardless of cover, he's so slow and his AI is so simplistic the strategy quickly devolves into just sprinting across the room whenever he gets close and taking potshots while he's coming back around. And with his comically clumsy critical attack, he'll likely finish himself off with his own grenades. Instead of a desperate game of cat and mouse between me and Barret, the boss is essentially just a big, slow normal enemy with way too many hit points. If more emphasis has been placed on hit and run tactics rather than just sprinting whenever her gets close, it could have been a fun fight.
Federova offers even more wasted potential. The arena in which she appears is both aesthetically threatening and perfect for a speedy, stealthy enemy. Federova plays some hit and run herself with her cloak and electrical attacks. However, Federova suffers from the same problem as Barret, in that some hilariously bad AI make for a stupidly easy fight. The magic trick? The stun gun. Yes, the best weapon to use isn't the heavy gun the game shoved in my face right before the battle, but the tiny little stun gun. Just stand still until she approaches, then run up and zap her. Not only does that do a fair bit of damage (I think-the game wasn't gracious enough to put in a health bar for the bosses), but it leaves her open for a few pistol shots to the face. All your stun gun darts will probably be gone by the time it's over, but I was able to beat her while barely moving from my starting position.
Contrast this with Vamp (the battle from Metal Gear Solid 2 anyway), and the potential becomes obvious. Vamp is much less confrontational than Vulcan Raven, and the battle centers on the player being the hunter rather than the boss. He's the one playing keep away now, taking shots with his knives and sometimes coming in for a big hit. While in theory Federova follows a similar pattern, Vamp frequently mixes up his attacks and thus requires you to pay close attention to his movements. Federova just hides for twenty seconds or so, then runs up and asks to be zapped. Forcing me to go find her instead of letting me wait in one freaking place would have made a world of difference.
Namir is somewhat similar to Federova, mainly because of his cloaking ability and his penchant for hiding. And while his movements are a little more erratic, he can still be felled by the same strategy of just waiting for him, stunning him with an electrical weapon (stun gun isn't quite as ideal since he likes to use his gun more than Federova), and unloading on him. His ranged attacks made me a bit more cautious when approaching him, but his AI is still very simple and easy to exploit.
The Ninja in the original Metal Gear Solid (MGS) follows a very similar pattern, and is actually pretty simplistic himself. However, the difference is that the Ninja's pattern will change somewhat as the battle progresses and thus forces the player to adapt. None of the different patterns are difficult (the Ninja was the easiest MGSboss for me once I figured out that I had to fight him hand to hand) but they at least keep the player interested. Namir on the other hand falls into the same trap as Federova did, in that he will always come to me and leave himself vulnerable. While his attacks might be a little more deadly, the trick to beating him remains the same.
The fight against the Hyrion Project is an absolute mess. The objectives of the first phase of the fight (kill the three drones surrounding the center structure) aren't even clear, and once I figured them out it was just another painfully simple fight. The most obvious solution is to run up, hit the buttons that make each drone appear, then shoot them. With the code from Darrow or some hacking it's also possible to use the keypad in the center and shut the whole thing down in one stroke. The second phase is even more confusing, since the game makes it seem like you have to do something in order to remove Zhao's protective barrier, when in truth it's just a matter of survival. Zhao summons some zombie troopers and a security robot, plus parts of the floor will become electrified. Just avoid them, since eventually the glass protecting Zhao will break on its own. At that point a few shots will kill her.
The easy comparison to make here would be with one of the Metal Gears, but honestly this thing is so ill-conceived I can't draw any meaningful parallels other than they are both large metallic things that make funny noises. While the first three fights had some potential, this one needed to be redesigned from scratch or completely eliminated altogether.
I really like boss battles in my games when it's appropriate to have them, and while some seem to be contending that Revolution didn't need them at all, I think they would have been a welcome addition had they been designed around the central concept of situation ambiguity that's pervades the rest of the game. Instead we got three battles with incredibly unrealized potential (again, probably due in large part to the disconnect caused by outsourcing their development) and one broken mess of a final boss. That is a damn shame, since the bosses could have been the icing on the cake for what was already a really good cake.