In a moment of synchronicity, I completed Doom 2 on Halloween. Doom 2 was very much of an evolution rather than a revolution. It's all in the same engine as the original Doom with one extra weapon (the good old Super Shotgun) and a bunch of new monsters to use it on. Also, this was the first of id's games to be fully commercial rather than shareware, so gone are the shorter, self-contained episodes, and instead we have one long campaign that you carry the same character all of the way through. That's not to say there's any particularly gripping story - this is still Doom after all - but it's nice to be able to play straight through without having to reset your weapons every 5 levels. And those levels are really the main dish here. You can tell that the designers had really honed their craft - these are generally well-paced, well-designed levels stuffed to the gills with monsters old and new and enough traps and secrets to keep you guessing to the end. There's much more mechanical variety on show here with levels that act and behave in different ways. Those new monsters also help, they're not just bigger and tougher (although they are that, too), but they also have different abilities, such as spawning other monsters, or resurrecting foes that you've already put down. Is it just more of the same? Yes, mostly, but 'the same' is so good to start off with, and there's just enough new stuff to give it a different feel.
Next up are a couple of official level packs for Doom 2. I don't have time to go through all of the millions of unofficial ones, but I'll give these two a go. First is Master Levels for Doom 2. 20 new levels chosen by the guys at id and created by community folks, many of whom who'd go on to get jobs in the industry.
I've not started Challenge of the Five Realms yet, but I am keen to...just got a bit more Doom to get out of my system first.