To be honest, until mid-way through the dawn of first-person shooters, I had never heard of the Duke Nukem series. My understanding is that they're relatively low-rent platform shooters, sending up B-movies and 80's action cliches. It really went nuclear, so to speak, in the mid-to-late nineties, when the gang at Apogee/3D Realms decided to cash in on the FPS craze, with the third game. And the result was a wild, intense, clever, raunchy, and surprisingly controversial landmark in action game history.
After defeating the bad guys, in Duke Nukem II, our titular hero (and before anyone asks, I have no idea what his day job is) is flying back to Earth, when his ship is suddenly shot down. It turns out that another alien invasion beat him back to Earth, killing, enslaving and mutating everyone in its path. So he has to fight through cities, prisons, bases, and space stations, to stop the ETs from breeding us into extinction.
The graphics and gameplay have their similarities to Doom, but in a lot of subtle ways they definitely take it further in DN3D. At the very least, you can actually tilt your head, jump, and crouch. I'm not 100% sure if this was the first FPS to have these now common features, but it was a rather silly omission from Doom. Some of the weapons are also imaginative, in that they aren't all just plain shooting weapons -- there are laser trip mines (that you attach to walls), pipe bombs (that you throw and detonate), shrink rays (that make you step on enemies you've reduced to the size of apples), and a freeze gun (that makes you go in for a kick). Similarly, the graphics across the board are crisper and more colourful than Doom. It's not the quantum leap between Doom and, for instance, Quake III, but it does make for a much less grim experience.
That doesn't mean, though, that your heart won't still pound -- some of these enemies are sneaky and tough enough that they scare the bejesus out of me! lol
My favourite element, though, is the level design. For one thing, there's a ton of interactivity -- lots of things in each room that you can destroy or play around with in some ways (especially with Duke's sardonic one-liners). Also, you can have a surprising amount of fun just riding subways and trains. A lot of the time, the levels AREN'T just drab factories, spaceports, and hell locales... they're realistic Earth-bound places. We all know what hotels, office buildings, bars, etc. look like... and they are uncannily replicated in this game. In the expanded Atomic Edition, this is taken even further... with a Mission: Impossible send up, a fast-food joint, a police station, a post office, and a tanker ship. Many of which, have you getting struck by lightening, or getting perpetually crushed by collapsing rooms -- I don't get that in many shooters, even ones newer than this!
A lot of flak has been raised, about this game supposedly promoting the murder of scantily clad women. I'm not going to pretend that just about every woman you see in this game, wears almost nothing, and is sexualized in some way... but you never HAVE to kill any of them. In fact, very often shooting them sicks multiple enemies on you -- so you can easily argue you're PUNISHED for killing them. So please, spare the moral outrage for something like Manhunt.
Anyway, whether it's on Steam or in abandonware, PLEASE give this a shot. It's a ton of fun.