I have played a lot of Mir2, but not a great deal of Mir3 - and when I did I was probably about 16 xD
What are the key differences between Mir2 and Mir3 & What is the early game like (similar or way different to Mir2)?
Key differences:
- Elemental system. Mobs (Not all of them) have different elemental weaknesses and strengths. Attacking a mob with for example a Wind strength of +5 against a mob with a Wind Weakness of -5 would increase your damage output. Calculations have been stated somewhere, at some point, don't remember them off by heart
- Skills/Spells. There are a LOT more skills in Mir3. For Wizard especially are also Elemental specific, you cast a Wind attack, it will hit with the Wind element. Other classes such as the Warrior, the attacks of HMoon as an example, it's element will adjust depending on the players strongest elemental strength...without any element the HMoon skill would 'look' White, add Fire, and it will look 'red' (Would also adjust what animation your target gets hit with).
- Bosses. On Mir2 you were able on a Wizard to solo WT at Lv.17 or sometimes less....Mir3, you will likely be looking towards at least Lv.40+ for any remote chance at soloing, and thats with Elemental defence on your items (As above, bosses will attack with a certain element, if you don't defend against it, you get much more damage). Don't expect easy mode soloing every boss in the game within the month, it won't be happening. Some bosses also come equipped with special mechanics, rather than a simple tank and spank and the odd Range hit.
There are a lot more differences. Such as beginning zones/maps/caves, there are much more variations of them. Previously you would have had OmaCave/Mines/WT. Mir3 you will have quite a few "Outside" maps to hunt in, as well as many variations of Caves (Such as FleaCave and AntCave, both being optimal for hunting for Gold, but provides a different map and different environment, with the same goal).
I will let others elaborate :P