One step forward, two steps back.
The single most painstaking thing is not being able to pick what map or game type you want to play for pvp. I shouldn't need to explain how game breaking this can be. You have no control whatsoever. You simply click pvp and join the que, and are informed when a "mission" is available, but are not told which one it is and can only accept or decline. You can either stay and play on a map and/or gametype you dislike, potentially with a team that is not balanced well, or leave and now they are down a player for the remainder of the match.
Not being able to switch classes adds to this frustration, because there doesn't appear to be any sort of team balancing mechanic set in place. You'll often find yourself ending up in games with 5 of one class, and/or no medics, or no engineers when they are vitally needed for the game type when going up against an enemy team who has the slightest bit of coordination.
You can remedy this somewhat by getting 3 others together and queuing up as a group of 4, but matches sizes are 10 vs 10. Do the math.
The only way to assemble more than 4 friends/guild mates together or do any sort of arranged guild vs guild match is to pay $15 a month for a subscription to the conquest AvA mode.
The core gameplay itself is pretty good and balanced. It plays pretty similarly to tf2, so if you like that type of gameplay you might like this.
PvE is okay. The high security missions can be pretty fun and challenging to do with friends, and while I haven't tried it yet, double agent sounds pretty fun where two enemy players get put on the npc side, almost like L4D style. But that doesn't change the fact that the level design and enemies get old pretty fast. Robots aren't exactly up there on originality or design. They even imitated or tried to imitate the portal esq styled humor for the floating orb drones, but it's falls so flat it's awful.
Both in pve and pvp the maps feel pretty bland. A lot of boxed building design, cement, and very little in the way of props or additional details. Payload gametype is directly lifted from tf2, which I don't have any objections to, but again it goes back to this game feeling uninspired.
The graphics themselves are good, but not great. The best looking scene you'll likely ever see is unfortunately the character class selection screen. If only the rest of the game had a look so inspired. The animation feels clunky and jerky at times, which makes you feel like you're playing at a lower fps.
For some reason the developers opted to not include first person view. It was stated in an interview that they found most players using 3rd person so they removed it. I don't know if I buy that explanation, but while it can be nice to have it to see around objects, being forced to use it isn't. The biggest downside to 3rd person combat is ranged combat at close range, particularly point blank range. In any fps being point blank means the enemy fills a large part of your screen and is an easy target, and can still be relatively easy to hit if they're trying to run around you. However with 3rd person the enemy can be right on top of you and they haven't really increased much in size on your screen, which makes it awkward trying to hit them as they run about.
Other design decisions puzzle me. For some reason you can't fly and shoot at the same time, yet you can switch to your weapon mid flight and switch back to your jetpack. You aren't able to swap your equipment loadout until after you've respawned, wasting valuable time. So many possible equipment variations and no loadout profiles. If you make another character he/she will have the same name as your first and share your guildspot, which is great in theory but it someone wants to use a different name for a different character apparently you can't do that.
It's become standard practice for mmos to be released in unpolished states with bugs to fix, content to be added, and issues to be addressed. This is really just a class based action game though with mmo features tacked on, so I can't extend to it the oft repeated "give it time" response that comes with the territory for mmos. Thankfully the game doesn't appear to have any bugs. At it's core the gameplay can be fun, but the mechanics around it more than often lend to frustration than enjoyment.