As a long-time WoW veteran, I have to say that at the beginning, the game feels fresh and enjoyable. However, the more time you spend playing, the more repetitive and boring it becomes. Some hero rotations feel odd and counterintuitive, dungeon spamming gets grindy, and the mechanics lack clear audio and visual cues.

Capstone dungeons are often a waste of time, since a single wipe usually means you won’t make it in time — and of course, someone always leaves without any penalty. Character progression is time-gated behind ratings, and for solo players, unlocking all hero talents heavily depends on the matchmaking system and who you get grouped with. On top of that, the selection of hero skins is very limited.

As a huge fan of Half-Life games, all that I want to say, Black Mesa is a really great game. I've spent so much a good time. I've played first when it was a free mod, then when Steam version was released, and now it was my third when Xen came out.
+ Climatic, beautiful and really good mapped locations. It's unbelievable it's still Source Engine. Devs really pushed it to the limits.
+ I really love some additions based on original Half-Life such as Surface Tension fights or Gangantulas chases.
+ Xen is just beautiful. I am impressed by how from the dark, ugly HL world raised that. When I first came out into Xen I've just dropped my jaw. Also, addition with HEV zombies or water plants is good change. It feels like Xen really lives right now.
+ Excellent soundtrack.
+ Really good voice acting.
- Sometimes little bugs, problems with physics and unnatural behavior of objects. Also, some vents had problems with the flashlight.
- I think AI still needs some work to be done. It's much better than was before Xen release. I've played on the hardest difficulty and I really appreciate Vortigants dodges etc. but still enemies sometimes have problems what to do. Now I'm working on achievements on Normals difficulty, and enemies dodge no longer and they are just stupid. I think it should be available on all difficulties. About AI I think it's just the problem of Source Engine. In HL 2 NPCs also had some weird behaviors.