A fun game in EDH is a game that requires you to really think about the resources you have and how to use them to the best of the situation. The "Chess" feeling is what I'm talking about, and it's a very great one. You and your opponent are equally matched, and you both have your own strategies to try and topple the other. There is other feeling like it.
Good sportsmanship is also another factor of making the game fun. I never ran into any rude EDH players (yet) in real life, and I have faced a lot of people using low tier and high tier decks, each of them being equally good sports about winning or losing. It's how people are enjoying themselves in a game of casual, low-budget cards with a couple of money cards thrown here and there is what makes EDH a great format.
What is "un-fun" is pretty much the opposite of the two above statements. Games that are too short aren't the most enjoyable, and games who a person would act like a spoiled brat, brags, or anything of the like, ruins the experience.
Evac and Mind Spring are pretty neat, but I honestly would wish the foil was one of the two. Also, a more iconic rare would be something like Djinn of Wishes, possibly replacing Denizen of the Deep.
I had a deck like this, except it used Auratog/Rancor. One thing that has helped and would fit in the mana curve is Opal Titan. It works against most decks, and protection is always a nice thing to have.
Since most Demons would require you to sacrifice dudes, perhaps a token generation sub-theme would work? Demonic Possession would make your own dude a Demon, and with stuff like Grave Pact you can use things that create tokens ... too bad there are no Demons or Ogres that create tokens (Kazuul doesn't really count since you can't make tokens at will.)
Good sportsmanship is also another factor of making the game fun. I never ran into any rude EDH players (yet) in real life, and I have faced a lot of people using low tier and high tier decks, each of them being equally good sports about winning or losing. It's how people are enjoying themselves in a game of casual, low-budget cards with a couple of money cards thrown here and there is what makes EDH a great format.
What is "un-fun" is pretty much the opposite of the two above statements. Games that are too short aren't the most enjoyable, and games who a person would act like a spoiled brat, brags, or anything of the like, ruins the experience.