Sure...
Each faction (a bit like in AOK) has one or more defined attributes that rules out the unit set.
For example the Danish are an Heavy Infantry faction.
What does this mean?
Their unit roster is mostly focused on heavy inf (like Landsmenn or Huskarles), while they are weak in most other aspects, especially cavalry (so you'll have to get heavy cav from the steppes or hire mercenaries), meaning that you won't get knights but only the crappy raider cav or druzhina...

Another interesting faction to try are the Italians.
Being a Militia and Late Tech faction they'll have to makedo with an overall low morale army and may need to bring numbers against an heavier foe, especially on early where they won't get anything better than MS and ILI...
Things improves a lot with time for them (halbs in high and other heavy units in late) but mercs and crusades will be a resource through the whole game since they don't get killer units.

On the opposite tactical side you'll find interesting the Hungarians, which are a low tech cavalry archer faction.
I found them great on early as with Szekely you can make a pincushion of most enemies and engage lighter foes, but their roster won't improve much in high and late.
Facing the Horde head-on with them is an unique challenge, as you'll have to use amored spears and get nothing heavier than feudal knights, but ranged cav dueling is very interesting.

Since many faction have a big weakness in their roster conquering territories that allows the production of some units is vital, so the steppes will be the favoured cavalry source for some players while others will want to take Swabia or Switzerland to get good infantry, though my favourite is Navarre to get the Almughavars, which are the infantry equivalent of Boyars imho...
Also pay attention to valour bonuses in the territories as they have a purpose now and gives suggestions about what you might get from the lands...

Finally, while the concepts are more or less developed this is still a beta so that while stable the faction aren't 100% shaped yet and you might find some unbalanced things exploitable by the human player...
Playing the game i also noticed that now no faction manages to get easily so big that they can kill anyone in a few turns, and some manages to exploit the naval superiority in an interesting way... I've seen the italians making viking-style raids quite a few times, they can be a powerful foe but usually the papacy manages to keep them in check and they have problems with rebellions... Ironically now they plays a lot like the real history and Byzantium seems to be their favourite crusade target