The entire base defense mission from XCOM Enemy Within.
Contains Spoilers.
The first time i played this, i was completely taken by surprise, as all of my troops were wearing the standard gear as i had unequipped everything from the soldiers i wasn't using. This time however, i specifically waited until i had a combination of MEC's, plasma weaponry, and Titan/Ghost/Archangel armour equipped on every one of my 20 or so soldiers before completing the "Assault the alien base" mission. Seemed to work out pretty well the second time around :)
![](https://i.ytimg.com/vi/Bi74qTm5sNE/maxresdefault.jpg)