My review: looks VERY good at this stage, with only a few minor issues to be worked out. If you don't know the game, it is basically about working RTS elements into a FPS environment. But it works VERY differently for each team: the marines have a commander who define squads, gives orders, decides the course of research, places structures, etc. The aliens are more organically organized: they can evolve to the builder class (the gorges) but have less need of team-wide coordination: their abilities naturally allow them to help each other without explicit orders. The result is a game which forces the teams to think about strategy: to plan their way through a map, controlling resources and other key areas, pushing forward and being driven back. Unlike simple CTF games or simple "objective" maps, it really feels like a progression of events: every battle means something. It's also suspenseful: lots of quiet creepy moments of transit that are suddenly punctuated with deadly ambushes. It's pretty intensive for a HL mod: lots of entities means you need a solid computer as well as a good net connection (56K doesn't quite cut it)
2.0 really fixes most of the major problems with previous versions. In 1.04, only one of the three alien "abilities" chambers got any initial use: the defense chamber. Now all three chambers provide abilities that are truly worth having. If anything, the new sensory chamber, which can cloak aliens and their structures (a fantastic looking effect, fading in and out as needed), is looking to be the new favorite.
The biggest change is that aliens can evolve to any creature without having to control hives (there are 3 on every map, and the aliens start with only one): it is the aliens attack powers that vary with the hives. Fades no longer have any ranged weapons until 3rd hive: but their blink ability is scary and very effective. Skulks look great in the way they rotate to match walls, flipping around crazily as they try to bite off people's heads. Onos appear much more often without it meaning that the marines are totally doomed. But it is truly scary to see a HUGE Onos decloak right in front of you, then devour you whole (after which you get digested, screaming at your fellow marines to kill the Onos and save you).
The marines haven't been changed as much, though the changes to the alien side makes them have to adapt their tactics. They now have eletrified structures, meaning that key elements of the marine base can be fully secured from skulks. HMGs are still uber powerful: but not as much against alien structures, meaning that the GL is much more prominent.
The marines also have an awesome new minimap in both always on upper corner form as well as a full map toggle mode. This allows new players to get some sense of the map, as well as seeing where their fellow marines and waypoints are located.
Overall, things are very good: it's a much faster game without ruining the element of suspense and "story," and many of the issues that led to boring stalemates in 1.04 are resolved. So far, the major problem really seems to be that the aliens are too powerful, and the comms seem overwhelmed with all the new things they have to keep track of (many more things need to be upgraded, and they have many more res to worry about spending properly, leaving little time to think without it piling up pointlessly). But perhaps that'll change as the marines learn their new abilities and teamwork options.
One last issue: Voice comms are very important: they really make or break some teams. It's certainly a must for any good marine comm, and it adds great atmosphere to things as well, like when a chattering marine down the hall from you sudddenly has his mike cut off and you hear his dying scream...