Opposing Force is awesome. Compared to the brilliance of HL1 it's a bit rough around the edges, but it brings something really important to the table: it's got amazing weapon and enemy variety, which leads to a huge variety of interesting combat encounters throughout the game.
Sadly, the lesson Valve appears to have taken from the negative end of their Gearbox collaboration is "put only shitty guns and like four different enemies in your shooters." :/
Valve took all the parts of HL2 (an extremely uneven game) and split them up into two parts to make the Episodes. All the bad parts went into Episode 1.
All the mediocre parts went into Episode 2.
Half-Life 2 just isn't as good as Half-Life was. I played Half-Life for the first time a week before my first time playing Half-Life 2. And then Episode 1 and 2.
The difference between the two is night and day. Half-Life 2's got the more compelling world--due to a lot of things like facial animations, sound design, art design, the visual storytelling (the literal storytelling is a lot of massive infodumping that sucks). It's a shooter on par with, like, Resistance 3 or Timeshift or something. Part of the problem is that all of Half-Life 2's puzzles are simplistic and physics based; they're not so much puzzles as "now make the physicy thing interact with the other physicy thing." Seesaws and floating barrels and weight on a platform and such.
Half-Life, conversely, is still one of the greatest games of all time. Opposing Force is amazing because it's still, at its core, Half-Life. I mean, the Pit Worm is basically the same thing as the Tentacle, but it's still awesome, because Blast Pit was one of the best levels in video game history, surpassed only by... what, Surface Tension?
I've enjoyed the humor in Shadow Warrior. Not every line is a winner, but it has great moments. Bunnies, the cop car, some of the fortune cookies.
The first 5 minutes of Shadow Warrior are funnier than all of Borderlands 2.
I think it deserves to be one of the most talked-about games of the year. It actually manages to be somewhat touching, in part because the entire game basically just takes clichés, eats them, and makes you watch. The end was wonderfully foreshadowed. Surprisingly good story; Lo Wang's voice actor and overall character actually kinda hurt it.
