Believe me you won't be disappointed playing opposing force. It is seeing Black Mesa from a different eyes so to speak i.e. from the eyes of Shepard. The puzzles in the game are interesting just like Half Life has, also opposing force has interesting new weapons and monsters. Play it and enjoy. You get to see Gordan, G Man. I like the part where you see Gordan jumping in to the tele-port stuff to Xen, wish they made it in such a way that you follow Gordan and help him to fight the monsters, and then have G Man give that speech to both Gordan and Shepard.Boot Camp is nice to play, actually I finished opposing force and then played the boot camp it was fun.

The sequels been rumoured numorous times... first about an HL2: Episode 4 to be made by Gearbox, and then in the game portal's only weapon, ASHPD; A.SHeParD, which made some people suspect that Portal's character was Shepard. Dammit, I want a sequel so bad. First I have to get a comp good enough to play HL2...

A pretty decent expansion for a great game. I thought it was neat how they revisited areas from half-life and took another route.
Although, i can't help thinking that black mesa wouldn't make any sense if you pieced all the maps together :)

p.s. the big finish was also a big monster fight.

Slightly glitchier; although I really enjoyed this alternative storyline centering on the Black Mesa Event. Great weapons and more exploration of the complex made for a great MOD that made it to publication[I think]. It did not disappoint me after having finished Half Life. For the life of me, can't remember the big finish.

I'm waiting for a sequel to this game. I can just picture Shepard stranded on Xen spending the rest of his life killing aliens, becoming feral and insane trying to find a way home.