To be honest D2M1 has become more of a "multipurpose" map than a simple Doom 2 singleplayer map from 1994. It is played everywhere in any way and anytime nowadays!
In-fact, due to its popularity, it appears that D2M1 is used in various game modes (speedrun, ffa, 1v1, in addition to the coop) especially in tournaments and challenges, and even in
survival games. (Killing Floor, Left 4 Doom, and I'm pretty sure I'm missing few ones...) And it's not only used as a reference, a dedication, a tribute, to remember how awesome Doom is or anything, but the fact is that the gameplay is pretty campy and forces players help each other. Plus, it offers an enjoyable playability when camping in the blue room knowing that they will (mobs) leave you and your team mates no choice, welding the door and waiting for mobs; quite exciting.
The way how D2M1 was designed fits perfectly with these kind of co-op games, now you're telling me that it still is played in coop but it's not as if D2M1 was originally multiplayer map.
Half Life 2 and Counter Strike had it as well, would have been made for fun though.
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Anyway, Nati is right, there was a time that D2M1 was regularly played in the tournaments - and I'm not even talking tournaments based on this map - back when ZD competitive scene wasn't in a dying state. Actually, you can consider it a challenging duel map if 2 worthy players are facing each others, or vice versa, ain't one if you don't own some experiences in there.
There is a website that FX02 and Sedlo are the authors where you could challenge any 'Doomgods' in here, since it had a subforum those addicted to D2M1.
For this reason, Sedlo, also known as Marijo Sedlic for his speedrun skills,
used to challenge decent opponents.
Go grab some demos in here :
http://www.doom.com.hr/public/doom2/demos/challenge/
Anyway, I also remember that one of the D2M1 tournaments was quite underfilled, which was the EU tournament with the most participants (about 32); everyone gave a try to it, was a good success due to the amount of forfeits being close to 0 (hazardously Sedlo was the one that forfeited)
Brackets:
http://doom.machata24.cz/zdeuro/2010_07 ... y_2010.htm
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Now, I do not write this all because I'm a D2M1 fan with such prediction skills, simply because I do know what their feelings are towards this map, because I like playing in the same spirit as those playing D2M1...
Skillwise, if you're a versatile duel player then you should be able to play every maps with no contraints instead of only focusing on a few maps that most of the new generation players doesn't care, but hey, I can fully understand those that were around enough to know what their states are goods at, get asked why you don't like D2M1, why do you only play it in the tournaments, and honestly I never really liked playing on Entryway / D5M1 in public servers or when inviting somebody to play some... it is so long and campy, that the player with which was hungering for some games, tends to leave / get bored because of a campy 30 minutes game...
I also empathize with those despite having given their bests but were never been as good as the elite players, may hate or not handle the map anymore.
Therefore, unless when I feel like playing it, the reason why I do not play D2M1 is because I'm somehow one of them.
Some players tried aka. the video below, some didn't, and some wouldn't like to play better opponents on it, whatever our reasons or definitions of duel are.
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If you think you're as bad as this player on the video then welcome to the group.
On the other hand, I can't stand the attitude that some people approach when they bitches on their opponents yet obviously doesn't know anything about the map, you cannot simply blame your opponent or the map itself because you didn't manage to exploit spawns / evade from them better than your opponent, it doesn't work like that, it's only your own fault, because as one_Two stated, chances are both get equal spawn anywhere.
After all, being good at this map is not given to everyone, it is not all about aiming, but you should be able to : be mentally prepared, learn to listen, know what your opponent is doing, grab the Plasma perfectly, evade etc etc.
To conclude, this video below shows an example of enjoyable, tight, dynamic and stressful tournament game, during which the two opponents had to adapt to the situations, the kind of game that I enjoyed because their situations were reversing :
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All this said, I'm not sure if this thing worth the 6 dollars he wants to give, knowing that you would have to deal with him if you get a loss heh!
Still looking forward to seeing some since I haven't seen D2M1 challenges / tourneys on Zandro yet, even if it ain't gonna be a so-serious deal compared to what I have seen on ZD.
Edit: if the last video that I posted does not appear, try it in ~15 minutes...
). But you know make money isnt easy, you have to beat me twice on map01, entryway, this map with chainsaw on balcony. Call it whatever you want. If you lose nothing will happen. 
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