If what you're looking for is more Half-Life--and you don't think you can wait on Valve to satisfy--then MINERVA gives you a bit of what you want. As much high praise as this game has received, though, I feel obligated to make a few criticisms.
The first is obvious: this is MORE Half-Life. Nothing here hasn't been done already, or better. It has a few problems of its own, though. Some encounters seemed almost designed to annoy. In several places the direction the player should take is not at all obvious. Of course, MINVERVA (the character) is always there to berate you for not seeing what should be, but isn't, clear. Speaking of which, what's worse than poorly-written monologue? Why, poorly-written monologue that's supposed to sound clever but comes off as ham-fisted.
Of course, these criticisms somewhat overlook the fact that, in the end, this is a mod. And as mods go, it's pretty good. It's also free. So if you've already finished Half-Life 2, might as well give it a whirl.