Adaptation Displacement: This wasn't the very first DotA version ever made - it's just the most popular (and most frequently updated). As to comparing it with other versions of DotA.
Awesome Music: As of version 6.60, "-music special".
Deny. Either part of the metagame that people should do, or a Scrappy Mechanic that encourages the "Make the game as unfair as possible for the other team" mentality.
There are *lots* of mechanics that fit into this category, usually mechanics similar to denials that were either bugs, or unintentional side-effects of the Warcraft III engine. Most of them are kept in because the devs and lots of players believe it adds skill, but many still believe they're arbitrary.
Catharsis Factor: Got trashed in a legit match? Start a single-player game in a bot-available version, select the heroes that just kicked your (team's) ass, turn on God Mode and kick their asses.
Game-Breaker: Item pooling. Eventually nerfed. The Fun Tavern (only available in versions where you can team up with and battle the AI) reveals that some heroes of past versions were even more broken.
A lot of items can be game breakers if you manage to get them early enough in the game before everyone else is buff enough to handle them; some particularly nasty examples are the Armlet of Mordiggian, Diffusal Blade, Guinsoo's Scythe of Vyse, and the newly buffed Agahnim's Scepter.
And, historically, a number of heroes have been this, due to the honest mistake of being overpowered when they were introduced. For example, the Moon Rider (whose Beam Spam has already been described) and the Sand King (who, come to think of it, can still stun you / slow you / shove his tail up your bum for the win, just not as quickly), but undoubtedly there have been others both before and since. Also, the Tauren Chieftain and the Batrider with Radiance... and a little before that, Kunkka.
Phantom Lancer, or as most people call him "Phantom Cancer" is a hard carry that only needs 4000 gold to be end game, can push all 3 lanes without risking his own life, oh and did we mention he has a great early game escape thanks to doppelwalk, which doesn't even clue people in to the fact that he switched places with a fake until the illusion dies?
Nightmare Fuel: The backstory of Nerif, the Oracle, is horrifying. And his voice does not help.
Paranoia Fuel: The Night Stalker's story indicates that he is supposed to inspire this in others. On the meta level, a good ganking team can make the other side afraid to leave their base for fear of death, allowing the carry to farm in peace.
Of particular note is the Stealth Assassin. Have sharp eyes, because he has an Invisibility Cloak and more often than not can Back Stab you to death in under three seconds (So does any other hero with an invisibility ability).
Same Hero, Only Mid, and the server chooses Lord of Olympia / Warlock / Goblin Techies. What fun.
Also add All Random and No Powerups, among others. The former is usually only played with friends; anyone playing the latter is "automatically" a Scrub.
What happens if someone leaves? They trash the whole game.
Most players starting out play like this: either their attitude improves or they get worse.
Usually they get worse first, due to finding some league/tournament rules, afterwards some of them get the attitude improvement.
They Changed It, Now It Sucks!: (Almost) Anytime a remake of a skill or hero occurs, even one that allows the "victim" to become competitively viable, someone somewhere will cry foul.
