While I certainly won't be as wise as Loinnreach in my post, I'll add my two cents anyway :)

I only bought BI recently, so I can't form a complete opinion on it yet. I played nearly only multiplayer, but I had a great time. I played about 8 matches, but not a single one crashed. None had any issue in it, excluding an horrible, horrible replay desync. Oh, and the night battle was slightly laggy, but nothing worse than that. Too bad, I loved the replays...

The unit selection is varied as had been mentionned, and while I did see 2 "spam" armies (One cataphrac and one huns horse archers), neither were very effective and were easily beaten (Sarmatian virgin cavalry > horse archer).I mainly played 2v2 as usual, but I haven't met a single rude person. In most games my ally and I actually worked together and supported each other: Most of my enemies did the same.

I'm glad that I'm able to have more diversity as playing as the Sarmatians also then as the Scythian before. And yay, more female units. I faced berzerkers, horse archers, roman infantry... Nothing came across as a cheap unit composition. Some horrible yes, but nothing "cheap".

For one, I love the multiplayer in BI, but I can't garantee it will be the same for you :)