There are a few problems, but If you want a unique multi-player experience that makes your heart pump, this is it.
Ill start with the bad.
There are definitely some short comings and if they added just a little bit more substance this game would be an easy 10.
The setup and matchmaking system are very old school and that is probably the biggest problem with the game. The matchmaking system works, but as soon as a host leaves you get disconnected. This can be very frustrating. Also, a PC game without dedicated server's just makes you shake your head in confusion. Connectivity wise it feels like an Xbox 1 game trying to figure out the internets.
Aside from these annoyances, when you are in the game gut ripping and head tearing, its just flat out gory fun. Sometimes there will be some frustration. Its very different from anything you've ever played before, and it takes a lot of getting use to using melee in first person. The best bet is to step out as a marine and just shoot things if it gets too hard,
Being a marine is the most fun because they are very powerful, but they are also the "prey" of the game. You will be running for your life and checking every niche the second you hear your radar blip go off. Marines are the best class if you like killing things coming at you.
Aliens where the hardest to practice, but once you figure it out they can be very deadly. Aliens attacks are very brutal and they have a tail swipe that lets them do some medium range damage. Aliens are also the fastest and if someone is nearby you can slightly see them through a wall. You can also easily see invisible predators. This is the class to play if you love charging in from an unnoticed location.
The predator was my favorite. Predators are a bit tricky to master but fairly easy to pick up. They have two vision modes, one for marines and predators and another for aliens. When playing a predator i must say it really feels like you are a predator from the original predator movie. You can use the plasma gun which makes for some really cool kills. Its kinda cheap the way they made the gun work, since you merely just aim and lock on for a kill. But its fairly easy to avoid it if you notice. It takes a while to charge(about 2-3 seconds if you want to actually kill someone) so for the weapon to be really effective its best to use it unnoticed. The predators don't move as quick as the aliens but they can leap great distances and sprint fairly quickly. Predators are sort of what would happen if you took your traditional RPG rogue, gave him a laser gun and heat vision, and put it in a FPS. Its a class that requires timing and sneaking to really get the edge.
The game does not get old fast because it really feels very different playing each class. The biggest frustration, if anything, is that the game could have been a lot better if some newer FPS elements where added. Something similar to a game-type where marines have to activate a generator while aliens try to stop them. Aliens would be turning off the lights and electricity, meanwhile predators would be raking in as many kills as possible off both sides. That's just an idea, but the given game-types, although cool, don't offer much "finality" to the game. Hopefully with a few patches and/or an expansion we could see some polish and this game could really excel to the top and blow away the competition.