Me and my gaming troupe grew weary of Arkham Horror too, so we stablished some house rules to fix it :
1- Pick investigators (before drawing the Ancient One), so nobody gets frustated from the very start.
2- Allow every player to discard his whole set of starting cards drawing a new set (only once).
3- Allow all players to trade Skill cards among them as they see fit, effectively pooling Skills before starting the game (and only then).
4- Play with the optional rules (Kevin sanctioned!): Face-up gates and allow investigators to have encounters in locations with open gates.
If this is not enough I would use the following house rules:
1- Allow Investigators to trade items in any phase, so the game is more dynamic and teamplay is more immediate.
2- Allow multiple expenditures of trophies in a single Arkham Encounter phase (like spending 3 gate trophies in a single action to bless 3 investigators).
3- Avoid Heralds and Guardians, since they greatly restrict gameplay and can add an awful amount of book keeping.
4- Ask for a volunteer to direct gameplay without playing himself as an investigator (yes, that means you).
5- Stop playing AH for a while, spend some time in rehab.
These house rules prevent frustation without being too unbalancing. The key to make the game more enjoyable is involvement though, and for that you need some sense of continuity to keep players hooked. There are several ways to give this "ongoing campaing" effect, the easiest being: Keep the defeated Ancient Ones aside and keep devoured investigators aside too, so those defeated AO or killed investigators are not drawn again; If you lose a game, then put the AO and investigators back in place and try again. If you run out of investigators you are busted and begin a new campaing, and if you run out of AO then... well, you just owned the game big time (never did it myself). We keep the defeated AO sheets displayed just like trophies in our gaming place, and the devoured investigator markers too as remembrance to the fallen. This simple gamestyle works like a charm on bored players, and took my troupe from boredom to an Arkham Horror gaming frenzy.
The jewell of the crown is my own complete Campaing System with custom Victory Cards, currently being polished with my gaming buddies. An experience system really motivates players, because without it all games end up the same, no matter if you win or lose: everything goes back in the box; with experience and campaing rules a victory becomes a powerfull stimuli to play again, mounting the interest of the players. I will post it when it's finnished.
Hope this helps.