If you're looking for the old Half-Life with zero changes except updated graphics, I think you'll find Black Mesa to your liking. Even with a few new areas in some (all?) of the chapters. Ever wanted to know what was inside some of the offices in Unforseen Consequences? Now, you know! Did you feel Office Complex was entirely too short? From what I remember of the original Half-Life (keep in mind, I played it when it came out in 1999), Office Complex featured a couple offices and then a giant stairwell with a sentry gun at the top. In Black Mesa's Office Complex chapter, you get to see more offices, cafeterias, and what I think may be "secret" areas with ammo, health packs, and batteries. Nothing overpowered. One of my most favourite chapters in Half-Life was On a Rail. Crowbar Collective definitely did an amazing job in vastly expanding On a Rail. I love it!

In a couple areas, I've noted little puzzles that make you have to run around a small area and look for something that'll let you continue. Nothing table-flipping, but I know I kept running around asking myself (aloud, no less) if I missed something somewhere. Turns out, I did. I feel it adds a little something extra, instead of just running around and shooting stuff.

One thing I absolutely love, though, is that not all scientists are one of 3 people. Not all guards are the same Barney Calhoun, and not all marines are one of two models. The updated graphics are pretty awesome, too! Another great advancement is ladder damage. Pressing E will mount/dismount ladders, so no worries about running off the side one one during a long climb and coming out with 20 HP.

For the AI, marines seem to try to flank you or shoot at you from several different vantage points, all at once. It can be challenging, but nothing a .357 magnum shot to the skull won't solve! Aliens and marines both can be a little derpy at times, though. I've noticed you can peek around a corner and shoot them in the arm, repeatedly, until they die.

One of two things I do dislike about Black Mesa, which may be a limit of the Source engine or my general derpy-ness, is that it's incredibly easy to get stuck on objects, like metal carts or boxes. The other is the achievements. One achievement has you "Help a barnacle and a headcrab find true love". You can save right before a headcrab jumps into a barnacle's tongue, and after it eats the headcrab you can load your save and do it again. You can do it 10 times in a row and get the achievement in 5 minutes. To me, achievements should be awarded for something great, not something you can do in 5 minutes.

The best thing about Black Mesa, by far, is all of your favourite chapters are there...and some chapters you may hate. *cough*Blast Pit*cough* And I feel none of the extra content was done in a way that's not in the spirit of the original. There's not a single added area I've seen, so far, that looks like it was thrown in to add some fluffer to the total gameplay times. The music is amazing, but I miss the HEV charging music.

TL;DR: The added content in each chapters is amazing, the graphics and models are amazing, the puzzles are great and add to the story without being too anger-inducing. The AI could use some minor tuning, and the achievement system can feel cheaty.