On A Rail, IMHO, was rather good, but too long, should have been about a quarter shorter, as all that train riding got boring somewhat.
The reason I prefer HL2 over HL1 is that there were no sections I disliked in HL2. Loved the airboat, Highway 17 and everything else. In HL1, I hated Residue Processing with a passion (only good thing - can be done fast), and didn't like Xen a lot either (awesome atmosphere and concept, sucky gameplay, clipping bugs on Interloper).
The reason I prefer HL2 over HL1 is that there were no sections I disliked in HL2. Loved the airboat, Highway 17 and everything else. In HL1, I hated Residue Processing with a passion (only good thing - can be done fast), and didn't like Xen a lot either (awesome atmosphere and concept, sucky gameplay, clipping bugs on Interloper).