What do you consider an ideal encounter?

There seemed to be a bunch of grousing last week about the types of opponents offered and their special abilities. Rust Monsters and Black Pudding both happen to have attacks that target gear rather than just hit points. Some gear was lost and it is a obstacle that will need to be overcome to complete the adventure. I think part of the problem was that there was not a change in tactics once it was clear that the normal paradigm was not in play.

Two weeks earlier the Dracolisk caused similar issues. There was some bad luck on attack rolls and saving throws but it seemed that there was no significant change in tactics when fighting something with abilities out of the mainstream. I admit I made a couple of mistakes regarding concealment that could have factored into things going wrong but I really do not think it was completely my fault.

This got me to thinking. If these types of encounters are aggravating and/or unfair, what is the ideal encounter from the player perspective? What kinds of opponents would you like to face? What do you consider a challenge? What lines should not be crossed? Character death in general? Level loss? Destroyed equipment? Death by Coup-de-Grace? Save or die effects? Targeting companions, cohorts or familiars?

To me, it seems like opponents that have different strengths and weaknesses make for a more colorful experience. I think it is dull to just have to hack your way though hit points. I admit, it does get old if every encounter has a situation where a character cannot be effective or as effective as their ideal potential will allow. The same thing every encounter gets monotonous. The key seems to be a mix. Some characters will shine in certain encounters while others will not shine as much. On average, everyone should have an effective role to fill.

My first reaction was to tell you all to just suck it up but that is not fair. The game should be fun. I am genuinely interested in what makes the game fun for you.