So I've now finished my replay of HL1. I feel it holds up well and I still enjoyed it. It does feel like a mix of different FPS aspects that one now looks for - puzzle solving, action, story and exploration. Quake 2 was more full on action as the puzzles were just grab the key. Unreal was more exploration mixed with action, but did have more advanced puzzles than Q2. Both of those were light on story and only had simple puzzles. HL1 throws it all together quite well.
The graphics still look fine even if things are sparse compared to current games. It does help one realize how much more effort is put into making even a simple room these days with all the objects one must add instead of just a few walls, a table and chair, etc. Nice amount of color and different environments, though I think Unreal 1 beats it (Though that might be because I ran it through UT).
While playing I noticed how the game was sort of broken into sections. You would have part of the story told in-game instead of cutscenes, then a puzzle section and then some action for it then to repeat again. The in game cutscenes help keep the game flowing and the action was always good thanks to HL1's squad AI. I liked how mercs sort of work together though I think one on one fights still have Unreal's Skarj as the best for this era of games. Playing too many tactical games also makes them easier to take out with a few quick nade tosses.
The puzzles were good because they were part of the environment. It was not just find the key or button to press though there were occasional buttons. Most were about manipulating things in the environment to get around the obstacle. Unreal had a few good ones (shooting chains to make a board float, etc.) but HL1 had more. A few times you needed help and the AI was not bad in defending itself as long as it had a gun. Of course one should never dispose of the AI help after their job is over just to get some ammo.
I'm unsure how often I have played HL1, but know it was many many times. I used to play it, Fallout2 and Red Baron 3D with my voodoo 2's. I remembered more of HL1 than I did Unreal or Q2. Even knowing it well it was still fun to go back through it. My xfire log failed me on the time though and shows only 3hrs, when I think it was at least 10 or so. Decent length for a game especially one you know your way around (I still took my time to enjoy it as I'm not into speed runs and still like to look in every nook and cranny).
The game ran fine for the most part except I did lose my skybox on the outside scenes. Not sure if it was always gone but I noticed it towards the end especially the chopper and tank parts of the game. I did skip the Xen portions as I don't like those as they become too puzzle jumpy for my tastes. Though this playthrough I think its because its more obvious the section is a jumping puzzle as opposed to previous ones in the game and something about the alien environment pulls that feeling out to me more than the nonalien sections.
I'm not going to mention any mods for HL1 as their are untold amounts - just check Moddb or Planethalflife or just throw in some quick google-fu. I've played way to much Action Half Life, Counter Strike, Front Line Force and Science & Industry with just a bit of Natural Selection. Also think I played some SP They Hunger and maybe a few others. Now to replay the expansion Opposing Force.