I posted this info in another thread, hope it helps here too.
MoP is a huge change from Cata, and I don't see how anyone can claim otherwise. I understand people not liking it, but it can't be denied that it's is very different. As other people have tried to answer your explicit questions I will just think back to all the things I have done while leveling, gearing and just messing around with 5 different toons.
Leveling
You can count on 3-5 hours per level, short if you are fast, longer if you are slow at questing. While you may do dungeons while leveling, any past the first one of each type will not get you much exp. The first time through has a couple quests to give you some exp. Personally I really liked Jade Forest(1st zone) and Dread Wastes(last zone). If you like lore Blizz did a much better job at good stories, and I found the questing engaging and interesting. By the 5th toon it was extremely boring, but the first couple toons I had a lot of fun in each zone.
Every zone also had a bunch of elites added in that have abilities that will easily kill you. Each type needs to be figured out and then properly killed. The rare will always drop a blue item, but its armor type is random. Each also has a chance to drop a loot bag that contains crafting materials. In addition each one has its own special item that has around a 10% chance to drop. This special item could be a leveling epic, a fun on use item, or it could have an in game use. I particularly enjoyed searching out and killing these rares.
The leveling felt stream lined instead of broken up like Cata was. You will remain grounded and not be able to fly during leveling. This may annoy you, or may force you to pay attention to your surrounding and enjoy it. I thought being grounded really allowed me to enjoy Pandaria as a Continent.
Dungeons
While in Cata early dungeons were hard, MoP dungeons are meant to be fairly faceroll. For those who really like a challenging dungeon there are Challenge Modes which can be really fun to learn. The harder of these can easily take an hour and a half the first time through. As long as you understand what each is for then it seems to be a good game design.
Scenarios
Scenarios are also fairly faceroll. They are faster than dungeons, but drop no loot. At the end of a random scenario you get a bag that has a chance at a low lvl blue, a dungeon lvl blue, or a low lvl epic. Scenarios have specific things you need to do in them, compared to a dungeon where you just go through killing mobs. There are a decent amount of scenarios, and if you enjoyed group quests in the past these should be fun for you.
Dailies
Most factions have a set of dailies associated with them. As you gain reputation you unlock more of their story line. Some of them are extremely grindy, like August Celestials. The one I enjoyed the most was the Dominance Offensive(Horde side) story line. As of 5.2 if you want to gear up you do not need to ever do a daily. A couple factions would allow for getting a couple pieces faster, but it is completely viable to gear up without doing dailies.
Reputation
With 5.2 came more ways to get reputation. Before it was just dailies, now you can do one dungeon and one scenario a day for a faction for rep. In addition there are rep tokens from various elite mobs that you can farm up. Finally you can use your farm to do work orders and turn in what you grow to earn rep with a faction. The current raid rep is earned solely through doing the raid, in any of its difficulty levels. The first valor item from this rep you can actually buy at neutral.
Gearing up
While gearing up at launch involved rep grinds it no longer requires those now. Doing a mix of dungeons and scenarios will get you pieces quickly. Getting epic hands/chest crafted helps a lot too. Your first week you get 1k valor, and in your second you can buy your first current tier valor item from the before mentioned raid rep. You have now just skipped over all those rep grinds the rest of us did! When you reach 460 ilvl you can do the first 2 parts of lfr. I would suggest heading over to the new daily hub, the Isle of the Thunder King. You can either do a set of dailies, join a group doing a special boss or wander the island until you find a treasure chest. During any of these activities there is a good chance you will find a Key to the Palace of Lei Shen. The first one is easily found each week, and then don't count on seeing another one until next week. Using this key gets you into a solo scenario loot run which will earn you Elder Charm of Good Fortune(I got 17 in a good run one time). You can use a charm after each lfr boss(or normal/heroic if you raid). These charms work on all 5.0 raid content. Each charm will get you an extra chance at an item for a boss. You can even run lfr more than once and keep using any remaining charms!
Old Content
Of course damage and health pools have gone up so more old content can be soloed. Warlocks as a pet class make a great solo class. In addition the new talent system really allows you to customize significant talents and glyphs for a specific encounter. A better question than what you can do would be what few bosses are left that you can't do? Honestly almost all are solo able now.
Brawler's Guild
If you like challenging solo content then head over to this arena and get a fight going! Each fight will test you in a different way, and each class handles each fight differently. This makes for a really fun event to head out to and knock out some bosses. Just note that as you get further ranked you will need over a 480 ilvl to beat the last few.
Farming
You can start farming while leveling, or never do it at all. Nowadays I only use my farm once a week or so. I'll plant whatever current crafting material I'm low on and save myself the time spent farming mobs or gold spent buying the mats on the AH. Some people hate the farm idea, some love it. I like being able to use it when I need something.
Well that's all I can think of right now. If you like the sound of all of these things, then definitely buy MoP. If you don't like the sound of these features then by all means stay away! As with any game it ends up being personal preference. I tried to cover a lot of things to give you an idea so you can evaluate what you like. I think the game design is the best of any expansion by far. The only downfall is the community on some servers has gotten worse. If your server hasn't gotten worse, then that's great for you!
Hope I helped and let us know what you decide on.
-Slatch