I think HL2 could have done with setting the scene more before dropping you in. Like in the first game, 10 minutes on a transport carriage really set the scene, it's your first day at work as a scientist in a multi-function facility.
I'd like to have seen some introduction film, like maybe people being rounded up, maybe a Stalker thing attacks innocents at a farm somewhere.
The thing that annoyed me about the storyline in HL2 is how all these figures come out of the woodwork, all these close personal friends that you've never seen before in your life. They can't just take a largely solo game like HL and put in a whole squad and buddy premise, not without explaining it a bit better. It's like you've just waved byebye to GMan, and your in some predictable apocalypse/big brother plot full of people you're supposed to know. Soz if they were actually in the first game, if they were then they played a very small part, certainly not enough for them to be so familiar with me
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I enjoyed HL2, infinately more than Doom3, but it didn't seem quite as homely as HL1. In HL1 you could be inventive and save a lot of bullets, or time, there was quite a bit of freedom in HL. In HL2 it seems much more of a shoot em up, very plot based. Not knowing what to do next and having to experiment or explore is what made HL1 for me, the way you could take over a gun emplacement or lay laser mines, or the way grenades reacted well - it was very engrossing, even when all you had to do was kill a half-dozen zombies. I really liked the gadgets in HL1, like controlling the crane, I expected more stuff like that, considering some of the enemies can be a real pain, like the Stalkers. What if they had a big wrecking ball, and you could jump in and smash the Stalkers off balance - a little more effective than throwing a park bench at them!.
In HL2 a lot of the freedom is really just throwing stuff with the grav gun, they relied on that far too much - personally I'd preferred to have seen more engine propeller traps, or dropping car traps - once your out of Ravenholm there's not a lot of that gameplay left. Why don't they set a game in Ravenholm, like the clean up operation, maybe catch up with the reverend if he's still alive. I think it would be very cool if they expanded on it, Ravenholm is easily the best scene in HL2.