Have you ever sat down to a game where one player pull out Oona, Queen of the Fae, someone else pulls out Lavinia of the Tenth, and you're left wondering whether you're even going to get to play? It's fairly obvious that Oona will have some combos hiding within, but you're fairly certain that the person who has Lavinia hasn't been playing for very long. Do you say something? Do you just play? Do you even want to?
EDH is a format that allows players to bust out the most powerful spells, or if you're like me, play the ones players like. The problem comes up when two players sit down to play and their play styles don't exactly mix. If the Oona player's deck is built to combo out on turn six or sooner while the Lavinia player's deck is just a concoction of bulk rares they had lying around, it's going to be a bad time. To say it up front, I believe it's a good idea for most players to have a 'bad deck' on hand when they go out to play. It's much easier for everyone to have a bad deck than for everyone to have a good one.
When I say bad deck, I don't mean it has to be absolutely terrible. It's just meant to be something where even if you don't win all the time, it's still fun for everyone to play with or against. EDH is a good place to use the cards you wouldn't normally touch to good use! An example of this is that my 'bad deck' a Startled Awake as its one and only mill spell. Why run a mill card if your deck isn't based around milling your opponents out? Because it was foil, it was pretty, and when I nailed an opponent with it everyone got a good laugh.
That's the big part of making a 'bad' (read that as fun) EDH deck. It's meant to screw around and goof off while some more competitive games are going on. There's nothing to say that your fun deck can't be good either! I've been referencing the deck as a 'bad' one, but I'd like to clarify what I mean. A 'bad' deck isn't oppressive or controlling, which makes it 'bad' against competitive decks, but it's fun otherwise.
I'd like to include a 'bad' deck that's actually pretty good. One of my friends runs what he calls his 'Library Library'. With the exception of basic lands, every single last card in the deck has the picture of a book or scroll on it. Every single last card. The deck gets crippled by competitive decks because it doesn't have a combo in it and is susceptible to large amounts of removal, but it's a blast to play against. The fun part is watching the books hit the table and do some weird stuff, so usually people don't smack it around too much in combat. The player using it gets tutors with Tamiyo's Journal, can make a sudden comeback with Grimoire of the Dead, or maybe he just filters his hand with Scroll Rack.
The part I really love about EDH is how much fun can be had, the memorable moments, and the use of weird cards I've never seen before. Things like that can't happen during competitive games, but that's not to say that EDH players should stop using combos! There's just a time and place for them: specifically against players who can deal with them and run some themselves. Whenever you go to a game store, there's always going to be some player who can't afford to build Food Chain or Nekusar, and is just running what they have. The players who can play more expensive decks more likely than not have the cards to make something a little easier to play against, and I feel like they should.