It's tough and rewarding. I'm stuck at the level where you fight the stealthed ACs right now so I am working on changing up my build, but I haven't been excited by a game this much in a long while!
Can't wait to climb the arena and try the multiplayer mode.
I love it. Got it on sale last week. It's tough, but fair. I would love more explanation of the weapon types (when should I use plasma? Laser?), but I guess it's something I need to figure out on my own.