If AoOs are interfering with your enjoyment of the game, then by all means trash them--or any other rule that is a hinderance rather than a help.
AoO works great for some people, and that's fine, but D&D got along for many years without them as well.
Just use a little common sense and DM's fiat.
--If your players want their characters to go charging by the ogre guards without giving them a thought, let them, but first inform them that the guards will get a free swipe at them with a hefty bonus as they go by--and, of course, you could always have the ogres try to trip them, move in front of them (opposed DEX rolls) , etc...
--Closing against a spear wielder? Tell them he automatically gets initiative.
--Spellcasting in combat? Caster loses initiative, DEX bonus, and suffers a penalty to AC--you might even give the caster the option of avoiding all or some of these penalties, at the cost of +5% chance of spellfailure per point of penalty ignored.
Anyway, just let your imagination and common sense be your guide, and you can't go far wrong.
Afterall, the whole point is to have fun.
