Now that I've played every class to some reasonable-ish degree (except summoner, sadly) I'm gonna give my impressions on all of them, so here we go!

Berserker: Simple and fun. You just go around smacking things
Bulwark: Greater Weapon Focus is pretty cool. This class is also pretty basic, like Berserker
Archer: This class seems to get mixed reviews. Personally I like it. I like sniping things, and volleying a ton of arrows onto everything. Note: I haven't tried sling archer yet
Arcane Blade: I find this class too hard for me at my current skill level. It just seems weak in melee and weak in casting and I can't get it anywhere
Brawler: The absolute best (maybe) class. It's so fun to punch things that should probably be incorporeal like ghosts and stuff. This class is also very strong which is nice

Rogue: Stealth is bad and dumb. The rest is pretty great though. Throwing knives can be pretty campy but idk I enjoy them. I like the poisons too, and Rogue's Tools. Oh, I guess traps are bad too :(
Shadowblade: Okay I lied, I don't know this class very well either. It seems like Rogue but with some other stuff I don't know very much about. Stealth is still bad and annoying
Marauder: It's like Rogue but less sneaky. It doesn't have stealth which is nice, but it doesn't have Rogue's tool which I like :(
Skirmisher: Skirmisher is a really fun and basic ranged class. Apparently though it has a lot of jank to it, and maybe it's because I play to horribly to notice, but I have never found it jank

Alchemist: The golem seems cool but after Arcane Eye stops dealing damage, your golem sadly is a horrible tank and is mostly used as a mule and/or a teleport, which is kinda lame. Alchemist bombs are kinda fun to use i guess. Alchemist gems are also consumables which is bad and dumb.
Archmage: Too! Many! Trees! To play this class optimally is extremely annoying--good thing I've never done that!--but I find it's kinda fun to invest primarily into a certain element and go with it
-Fire archmage is alright, Ice archmage is pretty fun imo, earth archmage I didn't enjoy very much, lightning archmage was really fun, i have not tried arcane archmage, thaumaturgist is fun, technomancer is also fun imo
Necormancer: This class is a bit intimidating, but once you get passed that it's super fun to play. The minions and spells are so much fun to use and feel so powerful

Summoner: I think this class is kinda underrated. It's summons are super cool and unique and all have different uses. Granted, I haven't played much of this class so maybe I can't say
Wyrmic: At first I didn't like this class, but it's sorta grown on me. I like all the different elemental abilities and their practical usage. Equilibrium sucks though
Oozemancer: I suck at this class and have never found it tanky when I played. I like my cute ooze bois tho :3
Stone Warden: Incredible idea for a class, you can turn into Harkor'Zun which is hilarious, you can finally use that stupid boulder throwing move the snow giants have. Absolutely amazing.

Sun Paladin: Nice strong melee class that also has a bunch of ways to heal. In general feels pretty powerful to play. Note: I haven't tried Fallen or Avatar of a Distant Sun
Anorithil: A lot of AoE spells, and circles are pretty dope. Sadly I haven't ever made it very far with this class

Reaver: It's hack 'n slash but with ranged spells too, which is pretty neat
Corruptor: I really like this mage. You get to cast bones and blood and disease onto things which is hilarious
Doombringer: Another fun and strong smacker of enemies like Berserker. Doombringer has a bit more range though which is nice
Demonologist: Too many trees! Osmosis Shield is a dope idea. I like the demon seeds too, I think they're neat. Apparently this class has a bunch of bugs/jank that I once again haven't noticed

Cursed: It's another berserker, except you're powered by raw, unadulterated hatred. This class is cool but has a hard time getting started
Doomed: Fun for umbramancy roleplay, honestly. You get *adorable* shadow friends to help you and you hate things so much they actually just die. It's great.

Temporal Warden: Get it? It's synonymous with "Time Lord", very funny. Anyways this class is amazing. Super powerful, cute--and also very powerful--doggos, and teleporting behind your enemies all anime-like
Paradox Mage: The name alone is amazing. You basically cast gravity and mess with time shenanigans all the time. Pretty strong feeling and fun to play

Mindslayer: Too many trees! But on the other hand you get to triple wield, which makes it 100% worth it
Solipsist: Too many trees! You have to be able to choose which ones you wanna invest in, which is kinda annoying but not the worst. All the trees are pretty cool though, except I don't like feedback.
Possessor: Okay this class is the best class because you get to be a cute snake :3, but also I kinda hate it because you get like 10 copies of your bodies and basically become immortal with the annoying drawback of being unable to heal your bodies conveniently. ToME is nice for having no consumables, but your bodies are kinda like consumables which sucks.

Sawbutcher: You blend things with saws. Amazing class
Gunslinger: You shoot things with guns. Amazing class
Psyshot: Okay, you shoot things with guns, but you're also psionic so you can do some really wack stuff. Solidify air? Have mechanical arms protruding from your back? Sure. I like this class
Annihilator. It's in the name. You get to shoot guns... and flame throwers, and grenades, and you get to bombard things, you can setup freaking turrets and have a giant mechanical spider to assist you.

Writhing One: You get the cutest of all buddies (other than shadows maybe) a nice humanoid mass of writhing worms! And you're a horror with a tentacle arm. But for real this class isn't amazing, but still nice
Cultist of Entropy: Dope name, but what the heck is even going on here? Too many trees?? Super confusing but also super fun regarding what you're doing. Manipulating the concept of entropy itself to waste away opponents? That's actually like the best idea ever. You can also spawn a deity from the VOID to come and pwn things.