So I finally got some time to sit down and play some more classes!
Yes, I have an 85 of all classes before anyone even asks.
So.... please keep in mind these are my solo PvE viewpoints; I've not done any dungeons or PvP yet.
1). Hunter.
*drool* I LOVE hunters now. All Pets can be any specialization type (you choose). I can finally dust off that old Ravager I've had since I made my draenei hunter. I tamed him at Level 10 and used him clear up until Level 70. Then Wrath came out and suddenly hunter pets couldn't hold threat worth crap. I eventually leveled him, but I had to use a different pet. Then they gave pets different specializations and Ravagers wound up on the Cunning list and he still couldn't hold threat. Now, I can give him Tenacity and he'll tank just as good as any other pet. Finally! Also worthy of note is that awesome awesome talent "Thrill of the Hunt", and also the removal of minimum shooting distance makes for much smoother play. Also, I picked the talent that gives me a 30% heal every 2 minutes which can be nice (especially since it heals the pet 100%). So far, my pet has never lost threat, and something (not sure what) keeps me healed between battles so it is very smooth.
2). Warrior.
Haven't tried Arms or Fury, but I played around with Solo Prot some. I'd have to say I'm loving the fact they got rid of the Rage requirement for a lot of our basic attacks. Gone are the days when your Charge is on cooldown and the only thing you have is Bloodrage and three over-eager DPS laying into mobs. You can at least build up some AoE threat even with zero rage at all! Rage doesn't take long to build up. Personally, I chose the Impending Victory, Double Time, and Shockwave talents, the last talent I wasn't sure what to pick because I was choosing talents with solo in mind and all of the talents on that tier are group-oriented (they all affect other players). Some things to note, I love how Thunderclap automatically procs a bleed (you don't have to Rend first, thus saving you a GCD) and I was throwing out Cleaves and Revenges all over the place along with Shockwaves whenever the cooldown was up. Double Time lets you round up a lot of mobs in solo play; you can charge two, taunt one and run over to a last mob if you want, not necessarily in that order. I'd have to say I'm pleased with the changes I've seen thusfar.
3). Death Knight.
Played Blood a bit, but I didn't like how much DPS it lost; killing mobs solo takes way too long. I tried Frost back early Cataclysm, but it was far too squishy for my tastes so I decided to give it a whirl again. I chose a bunch of health restore talents thinking it was still squishy, but the truth of it is, it really isn't unless you're rounding up multiple mobs at once, so I probably could have chosen other talents instead. I might look into that. The DPS is pretty dang good, I don't remember how much changed between Cataclysm and MoP, though, but I will note that my Death Knight was putting out better DPS than my better-geared Ret Paladin and was keeping her health up just fine. If I really got into trouble, I chose that Death Siphon talent, where you can use 1 death rune to heal yourself for ~12k health. Death Runes are constant, so it is more than enough. Even if it weren't, I still have Death Strike (esp with the glyph!). I'd have to say I'm pleased.
4). Priest.
Took my Shadow Priest out to kill some elite mobs in Dragonblight (those snakes). I didn't get a lot of time to test this yet, but I notice that some of her spells were hitting hard. I'm wearing 377 crafted PvP and using Ahune's Frostscythe (lol, I know, right?) and I was doing 34k crits with mind blast. Every Mind Blast gives me an orb and when I get three of them, I can nail a mob with a fairly strong leech spell (Devouring Plague). These two spells were more than enough (along with the occasional channeled DoT) to do the job. I wanna take her out and try some more against mobs closer to my level, but so far I like what I see.
5). Rogue
Tried my rogue too, a couple days ago. I love the new poison system (thank God we don't have to keep buying the stupid things). Much simpler and easier to use. I've always played Combat, so I'm going to say things from a Combat Point of View. They didn't change a whole lot, to be honest. It plays much like Cataclysm Combat did, though I seem to be doing more DPS. They sadly removed the "killing blow refreshes durations of Recup and SnD" or at least they removed it for Combat. The healing poison though, seems to be working fine if I stick to single mobs. I can always Recup if I fight 2 or 3 mobs at once, though. Getting the Insight buffs seemed much faster than before (I remember killing mobs and routinely only having Green... now I almost always have Red by the time the mob dies).
I did take my mage out for just a little, but hadn't had time to test it, nor have I had the chance to try Warlock. I've heard good things about it, though, so I'm going to try it soon. Hopefully they fixed Warlock; Cataclysm was some dark days for warlocks.