I really enjoyed playing as Hungary, I really liked the cheap, high attack croatian axemen that you could send against the enemy flanks in swarms. I think there is more variety as you go along. At the start of a campaign its all militia untis but as the campaign progresses factions get more varied. The Spanish factions get great skirmishers and Sword and Buckler men. The Scandinavian factions are very dependent on attacking the enemy since very few of their untis use spears. Novgorod is interesting to play because of their heavy cavalry and horse archers, they also have a lot of infantry that carry a bow or javelins in addition to their melee attack. I'm basing this off the Stainless Steel mod, but since it is the vanilla campaign just better I don't see why anybody would play vanilla Med2.
The only unit I enjoyed with Hungary were the battlefield assassins. The Hungarian Nobles, being medium-cavalry, horse archers had huge potential but they screwed it up by making them very hard to control (you had to watch them constantly to ensure they wouldn't run into enemy ranks, and they often disobeyed direct commands resulting in their slaughter). I think Hungary also had some nice heavy cav. but it's nothing special since basically every faction has got it. I however, primarily favor infantry in battle and Hungary really had some exceptionally weak infantry.

I did like their campaign most however, very challenging. I'm being unfair to Medieval here (forget if it was 1 or 2), overall it was a very enjoyable game and is my fourth favorite (after Shogun 2, Napoleon and Rome).