I finally finished Episode Two yesterday. This time, I set the difficulty level to "hard" directly. When I've played the other Half-Life games, I've always started on "medium" (or even "easy", I think), but this time I decided to take the difficult route the first time through. And Valve really makes you earn your kills.
A fun thing about Episode Two (and Team Fortress 2) is there is a set of "achievements" (or sub-missions); such as breaking every web cache in the caves, killing all the antlion grubs, etc. There is also a fun achievement involving the gnome you find at the very beginning of the game.
The first really tough part was trying to kill two Antlion Guards. You don't have enough ammo (even if you've fully stocked on the shotgun and the MP5) to take them out, so you'll have to be a little creative with explosive barrels and other things you can shoot at them. To make things more fun you have the antlions to worry about too.
The second fun part was the helicopter battle where you desperately try to find a rocket launcher just to realize that there isn't any. The point is to take it out by taking the mines it drops and throw them back at the helicopter. Ah, the joy of crawling around and being shot at by helicopters!
Then there is the Hunters. The first time you encounter them is when Alyx is injured, but the first time you have to take one out is later on when you and Alyx are attacked by a pack of them in a farm house. Also a fun scene, where you have to be a little creative with the gravity gun.
Then there is the final battle. You've reached the White Forest rocket base, but it's being attacked by Striders. And not one, two, or three, but at least 8 or 9. I didn't keep count. This is where the real fun begins. And to make it even more challenging, each Strider is escorted by 2 or even 3 Hunters.
This game is nothing less than a masterpiece. And you haven't really played it until you've played it with the difficulty set to "hard".