Seems like in the most recent patch, they upped the difficulty of how hard Advanced and Extreme were. While they were originally quite difficult, my group (barring any "misfires" at cars) was able to clear the unlisted "Impossible" difficulty in about 30 minutes or so. While over only 2 levels this may seem a challenge, try spreading that over the entire campaign. Insanity. I relish in it.
While you may think the game isn't worth $50, they will be doing with it what they did with TF2. Constant content updates in the form of more achievements, more weapons, more maps, more game modes. Valve will definitely start moving it away from a A->B type game and I forsee escort/rescue missions. Possibly even vehicles. The great thing about this new engine is how much potential it has. Once Valves programmers explore it more, they will bust this game wide open. If you want to wait for a price drop, that is more than fine, but you may be waiting for a while. Valve will definitely be throwing out content to help justify the price.
Also, don't forget the additional gameplay mode that we have yet to even explore. The Vs. portion of the game will be a whole nother can of worms. When you have bosses controlled by human players who understand ambush and tactics and timing better than an AI... I'm looking forward to this.