Agree. I recently played HL2 again with the new commentary (added because of the 20th anniversary) and it really shows why the level design is so good: a lot of play testing and iterative design. They really did the work.
Now I'm playing the Halo franchise and the difference in how boring and uninspired the levels are is really striking.
Mm. Halo 3 felt really open and expansive the first time I played it. Second time, I tried to explore outside the normal path and rapidly discovered that it was a very well disguised rails shooter.
But I've also gone back further than that in Bungie's back catalogue, having recently been playing Marathon 2 and Marathon ∞ (winner of the MacFormat(?) magazine award for "largest version number increase between successive releases") on Steam, and… well, 2 has still-interesting levels, but Infinity's levels are a spatially confusing mess.
