How long should a single player campaign be?

For a FPS with a non-boring story, I'd say 15 hours for the average casual player, dying a few times and a few hard spots.
Should be doable in 7-10 hours on a second run dismissing unimportant stuff when you know what you're doing and the hard spots aren't hard anymore.
That said, ∞ hours of secrets and replay fun is a big plus.

(Did I just described Half-Life?)

 

But Half-Life doesn't have any secrets to find. Plus it has little variation in skill levels other than the damage that enemies cause to you and the damage you cause to enemies (per shot). I can't remember, does it even have more enemies per skill level? Half-Life is really good (aside from the Xen levels, which are very well done, but no fun, IMHO), but I wish the harder skill levels presented more challenge for those of us who've played the game to death.

Look at Perfect Dark, for example. That game got skill levels right - the higher the skill level then there's not only more enemies (who give more damage, and are harder to kill), but some of the levels (in game areas) are larger in the higher skill levels, plus the higher the skill level the more in-game objectives you have to complete to finish the level. Plus when you complete the game on any of the three skill levels then you unlock a bonus mission (so three extra missions in total). Plus (and I wish this was in every FPS game) when you complete the game on the hardest difficulty, you unlike a fourth difficulty, where you choose the difficulty level, but setting the three options:

Enemy Health: from 10% to 1000%
Enemy Damage: from 10% to 1000%
Enemy Accuracy: from 10% to 1000%

Any game you play in this mode has all of the features of the hard level (i.e. all objectives, all enemies, and the full areas of the map), plus the three settings above as you choose. This has enabled players to create custom modes, and two of them (License to Kill (LTK), and Dark License to Kill (DLTK)) are very popular amongst the hardcore GE/PD fans.

License to Kill:

Enemy Health: 10% (Perfect Dark won't allow you to set Enemy Health to less than 10%)
Enemy Damage: 1000%
Enemy Accuracy: 1000%

Which means that the enemies can kill you in just one shot, and any enemy will die from one shot from you.




Dark License to Kill:

Enemy Health: 1000%
Enemy Damage: 1000%
Enemy Accuracy: 1000%


Now, even though you still die from one shot, the enemies are *very* hard to kill. Even so, some people still manage to speed-run though this game mode, which amazes me!

Plus Perfect Dark also has some fantastic cheats, not just the ones that make the game easier (Invisible, Invincible, All Weapons, Unlimited Ammunition, etc), but also cheats that again make the game harder, to add more challenge, such as Enemy Rockets (all enemies carry personal rocket launchers instead of normal guns), and Enemy Shields (basically enemies have shields/armour so they are much harder to kill). People have completed PD in hard mode (Perfect Agent mode) with the Enemy Rocket cheats, but I don't know if anyone has completed the LTK or DLTK modes with Enemy Rockets (that'd probably be about as impossible as you could get in a video game!).

It would be so great if other first person shooters had options like these, to add re-playability, and to challenge the very experienced players (I wish Bioshock 1 and 2, for example, had more challenging difficulty modes. But I'm so thankful that Goldeneye and Perfect Dark have so many ways to make the game harder (LTK, DLTK, enemy rockets, etc), as you never get bored of the challenge.

 

I agree with the fact that hl didn't have that much secret, beside the few hidden spots with gear, you can actually make it insanely hard with console commands or mods. Not as convivial as PD, but still quite easy to do.

 

Yes, I remember spawning enemies and friendly NPCs via the console in HL and Opposing Force (OF is my favourite of all the HL 1 and 2 games), it was fantastic setting up huge battles.

 

to me nothing is more disapointing than finishining a game in 1 or 2 sittings. then again alot games seem to be geared towards multiplayer anyways...maybe im just stuck in the times of games being hard as fuck and you got your times worth.