This game hates you if you are a new player
If never seen a game that is quite so against the "pick up and play" concept. Not even Dwarf Fortress or EvE online. Which is a damn shame because it's a really well thought out game in terms of game mechanics, theme and balance.
First off, a team of rookie marines utterly beats a team of rookie aliens. The standard shooting is much more familiar than the alien movement to the average player. Which is why you see the akward moment on rookie servers when nobody wants to go on the aliens side and everybody is pressing against the marine door in the ready room. I am willing to bet that most new player's first matches are on the aliens side, since they don't know anything past that tutorial, and it's a slaughter.
Secondly, the game tries to highlight rookie players and have rookies servers but really other people won't teach you anything. I have been told to play at times with more people (6PM + apparently), that didn't help at all. It was either friends that played together and talked amongst themselves or commanders that just gave flat orders and who knew the game followed them.
Thirdly, the community...isn't the nicest I've seen. During my first game I asked in team chat about which buildings do you usually attack first (I was an alien surprise suprise) and the immediate and succint response was "f off n00b". Now I know this was just some guy but I'll admit it slightly soured my excitment to play a new game. I won't list the racial slurs and homophobic statments but suffice to say that since the game doesn't like new players neither do the veterans.
Fourthly, the game is not learned through playing but by researching. This is the only profound negative opinion I have regarding it. If you want to learn this game you have to open the wiki and start reading and then practicing vs bots....practicing a LOT. Of course other games require you to research to reach the "depth" (stuff like min/maxing, speed running, best in slot etc.) but this game requires you to do all that just to "play" the game properly which is, in my opinion, horrible game design.
Chess takes 5 minutes to explain, 1 game to understand and a lifetime to perfect.
I am sure people with a lot of free time on their hands, copious amounts of tenacity and a generally eltist attitude (see people who say "Old school WoW pvp is good because 40+ buttons means that all the dirty casuals that dare enter an arena without 100 hours of training get filtered out".) will enjoy sinking their teeth in something that requires so much to get a working handle and even more to get good. Of course you can have a coach friend to rectify this but not everybody has this luxury.
It might seem that I hate the game but I actually respect it in a strange sort of way. It feels like a private club that's at the top of a moutain...a really high mountain that's covered in razor wire and mines. Sadly it just left one of the worst first impressions on me given how good the game is.
I won't be returning to it since it seems like work to get anywhere...and I already have work to do so I don't starve or freeze.