Looks like I might want to check out Chocolate Doom.

Well you can install the game through Dosbox and play it from Dosbox, you only need floppies with the game ;p

I've never used any custom/player created levels for Doom. Where does a newbie like me begin? What are the classic level/mod packs I should hit up?

Get the award-winnig stuff http://www.doomworld.com/cacowards/
And the standalone games
Chex Quest 3 http://www.chucktropolis.com/gamers.htm
Action Doom 2 http://action.mancubus.net/
Harmony http://rabotik.nl/harmony.htm

Thanks a lot, and thanks in advance in case there are more replies later.

Whoa this looks really good. Someone needs to make a "If Doom were to be released today" thread to complement that Quake thread.

Aside from rechargeable health, I wouldn't mind if there were more first person shooters like this, with similar movement style (speed + acceleration) of Doom. Looks like the closest would be Serious Sam 3.

Look up, at my first post. :)

Have you guys tried Stronghold? After blasting away hordes of demons for hours, I can safely say this is my favourite mod for Doom, ever.

There's Real Guns Advanced/Real Guns Hardcore, which adds guns and perks from the Modern Warfare games, as well as stuff like enemies going into last-stands and dropping fuck-you frags.

Aeons of Death v6 released, and I already miss the v5. Sure, Left 4 Dead with AI director on Doom engine is fun and crazy, but the "mobs don't drop guns" rule in normal game means you'll be running with the pistol replacement entire levels if there's no gun spawner.