Hey, Long time lurker, First time poster here.
I was interested enough in this thread to register, so I think I'll share my 2 cents.
Medic: Invaluable, made even better by the versatile (and lightweight)medigun. All that really needs to be said.
Firebug: My old favourite (from before the Heavy Metal DLC), sadly its much less powerful now, with the mob's health increase. It was a good room clearer, but lacking power and without the new infinite burn (glitch?), I sure wouldn't play it at all. Overpowered on the Patriarch because of the new burn time.
Commando: My favourite, but it feels very different since the Level Up DLC. In Heavy Metal it was "Priority on stalkers, crawlers, and Sirens. With good damage on everything else." I used a AK-Katana-DualHC loadout, and that worked very well, I could kill scrakes with the Katana, and had DualHC's for backup if I ran out of AK ammo. FP's were a problem, the decapp trick was doable with the Ak, but very hard to pull off if it wasn't going for you.
But that was the point, they were supposed to be hella powerful.
Now, with the FN SCAR-H, single shot is the name of the game, and it's low weight means its very common to see a commando with a grenade launcher or something. I don't want to sound bitter, but for single shot the SharpShooter is much better, the new M14 is crazy good, and with the headshot bonus, M14 is better than Full auto SCAR for damage dealing on the big guys.
Commando is back to the low priority targets role, like back in the bullpup days.
Support Specialist: Pretty good, the guns are soild, the extra blocks are great for interesting loadouts and carrying those big guns. lots of good damage on the big guys, but short range only, limiting it somewhat.
Husks are extra annoying at range, and watching your kills get taken by a SharpShooter is why I haven't yet got it past level 5 and into level 6.
Never a favourite of mine, I used to see a bunch of good ones back in the Heavy Metal Pack days, Great for Scrakes and Fleshpounds, needed very little money. I used to have a lot of fun as a commando in 2 man games giving them backup against crawlers, sirens, and stalkers. Fun teamwork there. But now... I see rarely any and maybe it's that weapons nerf that I have about, but those I have seen kinda suck...
Demolitons: The New guy, the Rookie, the Noob class, The Smokescreen, it is called many things, chief among them a room clearer and a boss killer with those Pipebombs. Also the class I see killing themselves the most, lol. They can do everything, and except for ammo shortages, troubles up close, they seem like a fun and balanced class. Of course, I might be biased because I can still see healthbars through all that smoke.
Sharpshooter: I hate to gripe, but this class is overpowered. Its really easy to level (my first to 5, my first to 6) and it has a tremendous amount of power with it's guns. This class needs some changes. The M14 feels like a souped up version of the commando guns, Use single shot, Aim for the head to conserve ammo, these are all things I have told new Commandos for a long time, and the M14 is much better at them than the SCAR, because of the big bonus for headshots. In Fact: Full auto SCAR to the face is LESS good that the M14 because of the small clip size, M14 wins.
And don't even get me started on the Xbow. It used to feel special 1 shotting Scrakes because you knew about their weird headhitbox, now, evey Sharpshooter can do it, making Berzerker redundant.
Sadly, it feels to me like the Level Up patch has Homogenized many of the gameplay corners the different classes have, Sharpshooter and Pipebombs have the big guys covered, leaving berzerkers as a liability. The M14 makes commando style crowd killing easy, while still getting very good damage on the big guys. And the M14 has huge ammo pools, making Support's 2 jobs (Being tight crowd control and big guys) better handeld by a Sharpshooter (cheaper ammo too). Only the infinate burn glitch is keeping firebug playable, Berzerker is already lost.
And medic, well, they don't count, but that dosen't mean I don't love them.