There is no depth to these games, they are bog standard run and gun shooters. HL1 only gets remembered and is did a real life setting well instead of being on mars or stroggos or something daft.
I actually can't remember the last time I saw you post without flaming a Valve game. Go on, try it.. say something totally irrelevant, about cars or something...
It'll just be "Valve's car models are crap".

Also the length of GTA games varies hugely depending on how much you do, if you just do the missions it's probably over in 15 hours, but you can easily put 100 in just messing about and doing the other stuff.