It occurs to me that while HL2 had its high points (the first 15 minutes, Ravenholme, crawling along the underside of that one bridge, the approach to Nova Prospekt, Breen) and its low points (sand traps, Nova Prospekt itself, Saving Private Generic Male #2, Citadel), episodes One and Two don't really have much of either. They're more like long stretches of anticipation mixed with periods of dull annoyance. Most of Two's memorable moments are handicapped by being extremely irritating (i.e. any time Hunters are anywhere nearby), and I can barely even remember what happened in One at all.
I guess part of what's so frustrating is that these guys seem to be kind of like Olympic swimmers of game design, only they're not going anywhere, they're just treading water in the same little pool they've been in since 1997. I mean the big selling point of Ep.2 was that it introduced one new enemy type (technically it also introduced the spitting antlions but nobody cared about those, and rightly so). So far the big selling point for Ep.3 seems to be that it has a boat containing a reference to another, much better game. Which I guess is fair, because at this point I'd like to play Ep.3, but I wouldn't spend actual money on it unless they put it in a box with at least two other games that were actually good.