Upon release back in 1994, Doom 2 carried the classic Doom gameplay to new extremes by adding new monsters, a double-barrel shotgun and John Romero's severed head behind a massive Satan face as the final boss - if you didn't know that spoiler by now you should read up on Doom lore.
If you have played the PC original you will notice a few differences. The most prominent is the new episode (which I'll get to in a moment). The second comes in the form of new health pack logos. Now they have a pill of some sort, in place of the red cross - as seen in Doom 1 Live Arcade. Although the cynic in me is yelling "Doom 2 for Live Arcade encourages the abuse of prescription drugs", because there aren't any doctors around, this is likely the result of the Red Cross trademarking the logo. Lastly, you revert back to a pistol at the start of each arch.
Doom 2 is much harder than the original - it almost takes on a thinking man's FPS moniker. Remembering the locations or health packs, ammo conservation, where to go first, when to tackle certain monsters, and which you may need to avoid depending on your health is vital in the higher difficulties.
There are a number of things players can exploit in Doom 2 to keep their ammo count up, while risking a little health. The first one is that monsters will fight if hit by a wayward projectile. It will turn around and take it up with the offender - starting fights between monsters is an exploit worth noting.
If ammo is plentiful it's a good idea to take rooms by using the doorway for cover and strafe shooting the demons inside. Rushing into rooms will typically end in you being bloodied and near death. In addition, cover is especially important when tackling the Arch-viles as they can deal major damage and their attack can only be stopped when you are out of their line of sight.
Unfortunately (or not if you like neutered monsters), this version inherited a few bugs from the PC original: barrels stuck in walls, Pain Elementals which can't release Lost Souls - rendering them harmless, even cute. In some rare instances, pistol troops can be turned invincible and will follow you around shooting you until you exit the room.
Doom 2 Live Arcade needed extra content to make it comparable in value to buying the PC version off Steam. As such, in addition to the 32 classic Doom II: Hell on Earth levels, developer Nerve Software has added a further nine - eight standard and one secret - as both a homage to the original episodic Doom and to add extra value to repurchases of Doom 2.
Nerve's levels are as good as, if not better than, Id Software's - incorporating ideas Id Software hadn't in their designs, such as using brown textures to create a dead garden and polluted jungles. The majority of the levels have inside and outside areas which take into account the dated mechanics, while feeling modern. They also cater to the old Doom cliché of having monsters burst out of a hidden room when you pick up a key or new gun.
Achievement-wise, Doom 2 steps it up with the most insane achievement ever: punching a Cyber Demon to death. This is a monster with about 4000 hit points (based on the PC version), and he fires rockets! Doom 2 also has achievements for easier tasks, such as completing the new levels on any difficulty and completing a single level with all items, kills and secrets.
Overall, while Doom 1 on the Xbox 360 featured very little to make it worth buying again, Doom 2 has a whole new episode which adds a lot to the experience. The new levels feel more up-to-date, with more outdoor levels which cater to the strengths of the platform and highly aged Doom engine. That said, after taking out the huge head in Hell on Earth, the boss fight is underwhelming. Still, Doom 2 is a must buy for any first person shooter fan - if only to learn a bit of history.