could you tell a bit or a lot about more tactics in MM2?
Is it only about :
- front line and back line characters,
- ranged attacks (archers more useful),
- rumor: an option to split party (like in Fate)
- critical hits (ninja)
Are these make much tactic possibilities?
In later M&M games there is no such things as front and rear ranks. In MM2 the size of the ranks (both the party's and the enemy's) are based on terrain. In narrow corridors only two character may have room to fight in melee, for example.
Archers make for good buffer characters since they can wear most armour and they are equally effective with a bow in front as in rear.
Robbers can get backstab attacks and ninja critical hits, but only in melee. Ninjas are restricted to Ring Mail and can't use shields, so they tend to have poorer AC than Robbers and Archers, making them more vulnerable in melee.
You can compose the party any way you like as long as it contains at least one player character. This is especially useful when doing the class upgrade quests.
In addition to your party having more options, the enemies are also much more varied in size than in MM3-5. You can face anything from 1 to 255 enemies, and the combinations are virtually endless. And with loot going from +1 to +32/+64 (depending on system) and most of it being alignment restricted means there is always the possibility of finding better loot.
All in all this makes MM2 my favourite of the old M&M games. It's only downside compared to MM3-5 is that dungeons are not saved when you exit them and are respawned if you re-enter.
And most importantly: is level scaling tolerable (although I heard about great imbalance later)?
The level scaling is tolerable, but noticeable. I don't think it's imbalanced, since it prevents you from facing enemies that are much higher level. IMO it tends to make the game too easy in some areas.
But some areas are scaled too high, since the fixed, non-scaled encounters are too weak. So if you enter the Ice Cavern or Nomad's Rift (which are off the beaten track) when lvl 30 there will be huge discrepancy between the fixed non-scaled encounters and the random scaled ones.