I've been in RP for quit a while, though this is my first time playing a full fledged "must kill everyone" complete villain.  I "grew up" in the Alliance era of things, with the Onslaught type of villains.  I saw their advantages and what was romanced about them, but I also saw their flaws which caused them to go extinct.  I see the polar opposite now, the very theatrical villains in choreographed stories who wish tell epic stories, and I see how difficult it is to bring such a project to complete fruition.  Neither are good nor bad, merely different ways of doing things, each with their strengths and flaws.  I should like to be somewhere in the middle of these two extremes.  

I want to kill everything.  And I want you heroes to enjoy it.

That, I believe, has been a major drawback to hero/villain interaction.  As a matter of sportsmanship, you are pressed into responding to any challenge and any threat.  But, as a storyteller, there are things you do and don't want to do.

Example:  
Thanos may drop out of the sky and land on your house, and I believe you would accept that attack.  But what if you liked that house?  What if that house was a plot device you enjoyed?  

Example:

What if I want to attack your family and kill your baby?  Well, Thanos might certainly do that, but what if you were really enjoying writing about you and your pairing's new baby and didn't want to stop?  

Sure, you could rebuild or resurrect.  But without a good plot behind it, then it feels like a chore to just get it over with so you can get back to your enjoyable status quo.  I'm not saying losing shouldn't have consequences, but at no point should RP be made less fun by other RPers.  That's counterproductive to all of us.  I think that's what ultimately made the Alliance-style of villains go out of style.  Net-fun went down.  They exhausted their food supply.  They did not tend to their fields.  

What if we treated this issue more like poker?  In poker, or other gambling affairs, you decide what is put at risk.  You choose to hold or fold. 

So, as Thanos, as a mad nihilist who wants to kill everything in the universe...  

If you say, "You can destroy anything you can find, except don't find out my secret identity.  I don't want to do that story yet.", you may rest assured I won't do that.  And within those parameters I shall, as a matter of sport, endeavor to raze everything else to the ground.

A villain serves to challenge the hero, but more so a villain serves as an agent of change.  I am here to shake things up.  

I'll attack Asgard, so that it can be sent back in time and the whole Asgardian cast can have a wild west adventure.  
I'll kidnap and enslave you, so that your character can become a cyborg assassin (I tend to do that).  

I'll kill you so that you can have a trial by Hela before returning to life with a white robe.  

I'll be defeated so that heroes may have a civil war over what to do with me.  

I'll destroy Attilan to set off a new hostilities between Inhumans and Mutants (oh, wait, did that already).

I look forward to killing you soon.  (And so will you.)