A short and exciting journey which could turn out to be the last one through crumbling city 17....welcome back Freeman!
+Same great gameply in shorter doses
+Nice and shiny new Source Engine
+Low req.
+No long boring stretched out sequences AKA airboat of HL2
+Have someone to kill zombies/combine with!Its AI Co-Op!
-have to admit...its is kinda short
-steam can be problematic (rarely though:))
Overall, its upto you to decide if you dont mind paying $20 for around 5hrs of gaming...me i already made the jump and iam quite satisfied.Better 50%of something than 100% of nothing :P
PS
its got hl2:dm and HL:S DM so if you dont have HL2, its an even better buy!