On the whole, Half Life 2 is less vomit inducing than the first. Don't get me wrong, the weird movement code and the way you always feel like you're sliding around, even on dry land, is nauseating in its own way. But there's nothing like that horrible reactor sequence at the start of the first game.
Despite the hype, HL2 was mediocre. The physics felt very gimmicky -- you couldn't do much with them, and all the "physics objects" were constantly in the way. Psi-Ops uses the same physics middleware as HL2 to much better effect. The story... Well, the story was basically non-existent. Don't get me wrong, there were a series of linear scenarios the game prodded you through, but there's no more story here than there was in Doom. The graphic engine was at least half a generation behind Doom 3, and while the art direction was very consistent, it was also a bit generic. And don't get me started on the load times. The worst I've seen since Road Rash on 3DO. I have a 10K RPM HDD and 1GB of memory -- there's just no excuse.
Overall, it kept my attention enough the I completed the game. Was it worth the full $20 I paid for it? Maybe. I'd be more comfortable with $10, or maybe up to $15, since I have no right of resale.
Speaking of which, Steam, apart from the game, is an annoying piece of shit. It stays resident after you exit the game, forcing you to close it manually. It bombards you with the same survey day after day, even after you've already taken it. It pops up "news" that you don't give a shit about. I'm very much less than thrilled that I'll be stuck with it again for the upcoming Sin Episodes.