Enchanting fan made masterpiece, released at a right time.
The fact that the game is a fan made freeware definitely provides immunity to criticisms that would in other case apply to some minor technical flaws. What matters in this aspect is that it created a perfect balance between being faithful to the original and taking advantage of what Source engine could offer in addition to that. Yes, Black Mesa is well playable recreation of Half Life, unfortunately it lacks the cosmic levels of the original, but what it does offer is more than enough for what it costs. All my respect goes to the folks involved in its creation, and to Valve as well - for the original and its permission to hand it to the fans.