I could only play a few matches last night so I can't fully talk on the subject quite yet, but my impressions so far aren't good. Being a merc wasn't fun at all and being a spy felt overpowered. It's ridiculous that spies have lethal guns and their melee is (or at least sometimes is) a one hit kill even from the front.
You should feel powerful as a merc, like a hunter. While as a spy you're the prey that has to outsmart him... well, if you can just run up and punch a merc in the shoulder and he dies then there's no "smarts" involved. Maybe they have a real spies vs. mercs mode that's unlocked later, but from what I played, it felt like a lame version of tag. Spies should only be able to jump on mercs' head and break their necks from behind, no guns, knives, cloak, etc BS. Are any fans of the old games enjoying it? Does leveling up the merc help at all? Even if it does, the level design feels lacking too IMO.