I don't think there's such a thing as 'the perfect game' where you can feel totally immersed even if you design it yourself. Chances are, there's going to be something that simply can't be fixed or put in due to code restraints.
Or later on you find that something you wanted for immersion, like the example requirement to eat and drink every 30 minutes, turns out to be something that's more of a hinderance than helpful. (How long is a typical blight hunting session?)
It's extremely difficult to try and stay immersed in a game when there are so many bumps and hiccups that is often very difficult to explain away.
Multiple game mechanics that just don't feel right, players that don't follow lore or RP something you as a player don't want to follow. The 1337 crowd that is only interested in number crunching and playing a game, which thankfully is not rampant in Istaria. It's difficult, but every so often you get those little sparks of "I'm there" and for a few moments, the game is what you want it to be.