1) No cut scenes, don't make Gordon talk, don't give away details about the G-Man in any way except slowly, with even more questions cropping up as there answered. The awesome action could be stand alone, but its held together by a sparse yet high quality story that leaves you with questions to hypothesize with your friends about. Basically keep it up, but for the sake of my sanity, please have a significant revelation in Ep 3 about what forces are at play, cause im dieing to know
2) Stop showcasing the physics engine, and just use it. In Half Life 2, the engine was unprecedented in quality, so showing it off is fine. Now, make it feel like your just making a awesome game with the engrossing experience of realistic physics. Gordon Powered Rockets breaks the suspension of disbelief.
3) Your not a vehicle driving game, but you do push the envelope. Try to use driving more sparsely, to mix things up instead of changing the formula. Think of driving like a mini game.
4) Give us a hint of Xen. I would love to see it in the Source engine, and would return the sense in Half Life 1 of a truly alien existence out there. Half Life currently feels a bit too terrestrial.
5) Add more Alien monsters and weapons. Again, Ive almost forgotten that were dealing with a strange alien world with things on the edge of imagination. I miss the Egon cannon, the Gauss Rifle, the Hornet Gun, and strange, intelligent aliens that are trying to murder me in strange, alien ways. Opposing Force has some great inspiration. And excellent job on the hunters, but even they feel more like advanced, totalitarian government technology instead of an alien menace.
6) Add weapons that arn't of the, "Its in my sight, pull button, and its dead" vein. Bugbait was great. Tricky things like satchel charges and remote mines really enrich the experience for me
7) The Black Ops enemies were awesome. They scared the crap outta me, and I had to get truly clever to overcome them. Any chance on seeing them again?
8) Don't make a context sensitive cover system. Just do it manually, where your less likely to get hit if you peek out just far enough to see your enemy whose not hiding.
9) I hate to go against something thats such a classic HL thing...but fix the flashlight. Flashlights don't have 30 seconds of power, nor do they recharge like that. Theres scary situations with it, but it feels contrived. Maybe the light sways wildly when your being attacked in melee?
10) If what I say seems wrong, ignore me. You guys are professionals, artists, and generally awesome.