Sounds like a fair (or even higher-than-expected) score, given all the problems that they single out:
Rehash of Half-Life 1
"With that said, many of those tricks feel more than a bit familiar now, and the game itself is saddled with a disappointing story"
"Half-Life 2 doesn't revolutionize the genre, instead sticking with the familiar formula of run-and-gun action, occasional puzzle-solving, and scripted sequences established by Half-Life"
"Half-Life 2 settles into a more conventional and familiar style of play. Aside from a detour through a deserted town full of all sorts of booby traps, there are a lot of echoes of the original Half-Life in Half-Life 2--so many, in fact, that there's a strong sense of déjà vu at times."
"Meanwhile, you'll be armed with a formidable arsenal, most of which is recycled from the first game, such as the submachine gun, shotgun, crossbow, and, of course, the ubiquitous crowbar. These weapons haven't changed much, and they feel roughly the same."
Teammates boring, with poor AI
"You never really develop any attachment to your teammates, though, as they tend to be very disposable, and replacements are available at regular intervals. And teammates have a tendency to get in your way in cramped interiors--while they'll slowly move out of your way, it's still a little annoying."
Story disappointing, many unresolved plot threads
"Surprisingly, Half-Life 2's story is one of the most disappointing aspects of the game. The first half of the game feels a bit unfocused, while the second half seems rushed. Even worse, the story leaves behind a mess of unanswered questions, and it doesn't touch on any of the lingering questions left over from the first game."
Enemy AI is worse than the first game
"Another surprise is the somewhat disappointing performance by the game's artificial intelligence. Even on the tougher difficulty levels, most of the humanoid enemies don't seem to show the same kind of intelligent behavior that they did in the previous game. They'll seek cover and then peek out to fire, but invariably they'll charge at you, making it easy to take them down."