I have finally bought it on the last sale and I finished playing it yesterday. It's a decent Half-Life reimagination that is well worth the time, but falls apart once you reach Xen, just like the original.
This is not 1:1 remake, many maps are changed in various ways, but they artistically and gameplay-wise stay true to the original. Overall, it's improvement in most of the cases. Maps are often larger and with more events going on. Weapons and gameplay do remain the same as in HL though, and so do enemies. This means that all pros and cons of HL are still valid, including being a bullet-sponge yourself, the same applies to hostiles. Moreover, the whole game is a long corridor that you follow. Pacing is nice with both action and calm moments in-between.
Graphics are vastly improved and are pretty, although still feel dated due to Source Engine limitations. Especially the other worlds look good now. Music is good and plays only in key moments.
However, once in Xen, which is late game, the game becomes somewhat frustrating item finding to activate doors. The last chapter is especially frustrating due to being almost solely a long repetitive platformer with few fights once in a while, and a lot of waiting and item finding.
For the price on sale it's certainly worth getting. If you have played Half-Life before then know this is an overall improved version of it. If you've never played HL then it's a decent shooter/platformer with interesting setting and quite decent gameplay although extremely linear.
I will add a mention of multiplayer, which is certainly not worth even checking out. It's like HL2: DM but with worse maps and weapons. MP consists only of DM and TDM and a few small maps. When I checked online there were only 2 servers with people (6 and 7), so it's not popular either. Additionally, it crashed before I could even finish a match, while SP never crashed in my playthrough.
Would I recommend it over the original if you are new to the series though? It's a tough question. The first 2/3 of Black Mesa are superior to the original, but the last 1/3 is worse because the worst parts of HL got a lengthy extension.