Doom 3 had interesting enemies - wall running demons, chainsaw-toting zombies, disembodied flaming flying heads, etc.
Half Life 2 had two types of guys with machine guns, a couple vehicles, and slow-moving zombies that could be taken out with one or two pistol shots.
Whoo-dee-freaking-hoo.
Anyway, Half Life 2 is simply unplayable because of it's
absurd level design. I simply can NOT get over this fact, and I can't believe everyone else can look over it like they do. For instance, after (spoiler below)
you come out of the portal out of the timewarp, and the resistance is just beginning, one part of the level is about 100 feet of the doctors lab. Then, you get another 100 feet of open space, where you just watch Dog kick ass (while you stand around and do nothing). Then you walk into a building, and get another 100 feet of the building. That is just plane ridiculous!