IMO Halo and Doom 3 still haven't earned what I payed for them. Repetitious games with dull gameplay. Again, my opinion, but while they're great I couldn't say they were worth their pricetags. Games like half life are too easy because they're modable. The actual game itself, Half life, is sorta decent, I'd say it was worth about what it costed when I bought it. A game like Deus Ex I'd say goes a bit above and beyond because you can play through it multiple times in different ways and it feels new each time. Strategy games are usually worth quite a bit more than you pay for them if you're into strategy games... games like Warcraft and, for me, Command and Conquer Red Alert. Role playing games usually offer immersive experiences that can take hours out of your life and that makes them prime candidates too. Everybody remembers final fantasy seven when we talk about RPG icons, less people remember six, some people remember Earthbound, all great games that are still great to this day. I'd consider those worth more than I payed for them (especially considering I didn't even pay for some).
Action titles... less so. A game like True Crime or Messaih or Grand Theft auto can be screamed through in a day or two without really going out of your way to destroy the game, and don't always offer a lot of replay value. Grand Theft Auto Vice City was a great game the first run through, good story, fun gameplay, unique missions, but when it came time to replay it or collect all of the dinky little secrets I got bored. I'd say it was what I payed for it. Same goes for Max Payne 2, a game that I thought was great, but that there was no point in replaying. Same goes for Doom 3, although I thought it was less than great.
I figure it all comes down to entertainment value. I think of Doom 3 and Max Payne 2 as movies more than games, and compare their prices to them too. A ticket at the door might cost you $7.50, popcorn and a drink and a couple snacks might cost you $10 more, and that's close to twenty dollars for two hours of entertainment. A solid action game will get you at least 10 to 15 hours, although the novelty tends to wear as you play through it.
Anyway the summary is that I think most of the RPGs and Strategy games I've played were worth more than I paid for them, but most action titles are only worth the money you shell out for them, some being worth less (Doom 3 is pretty, but not $55 worth of dark metal hallways pretty). All FF games I've played, Deus Ex, Max Payne, Max Payne 2, the original Grand Theft Auto... and some others.
Edit- Oh shnap, totally forgot about Carmageddon. 1 and 2 were awesome, 3 was prettier but less playable. 1 and 2 were worth way more than I paid for them, 3 was just sort of "extra."