People need to give the game a chance in all honesty. I've got 155 hours on MNC and everything which has been said so far isn't really a problem once you learn how to play the classes and get to grips with the objectives. In the first couple of hours i too was "Assassins are OP" amongst other things, but once i knew my way around the basics, half of the things i had worried about vanished completely and the other half fizzled away as i got more experience. It's a great game but people have to want to jump over the first hurdle before it really shines. It's a very steep learning curve if you've only played for an hour.
Assassins are so easy to find and kill when you know what to look out for. They are glass cannons and very loud ones at that; the cloak gives off a very noticeable sound (it hums) and can be heard from a good distance away. If you wear a headset then you can even tell where it is coming from before the Assassin is anywhere near you. I have often heard this sound, turned on the spot, and fired in the general direction which more often than not has grazed the target and after that it's just a case of killing them before they can rush escape.
Assassins are great for new players because they can pick off other new players quite easily, but once those people know how the classes work then the newbie Assassins don't stand a chance. Even jumping can stop an Assassin in their tracks, trust me when i say there are many counters to that class.
As for Juice it can be stopped if, yet again, you know how. A lot of classes have throw grapples and charges, so knocking them off the map is often the best way to stop a Juice rush and it's a lot easier than you might think too. Most people think they are invulnerable but i've seen several Juiced players go down through concentrated fire-power, turrets going crazy on them, etc. It gives you a boost, yes, but only for 10 seconds and during those 10 seconds you can still take a ton of damage and be effectively shut-down.
Lastly, the browser. With the influx of players over the free weekend the browser simply stressed out and buggered up; had something like 20 people trying to fill a 1 player slot on every server available, which clogged up the entire thing. Said issue has been resolved now and all is back to normal.