Heroes 6 was designed with multiplayer in mind because they really wanted H6 to be more competitive than the previous games (hence the resource change, towns/armies being so boringly similar, 100% hero customization). I personally found it extremely boring, the dynasty was no incentive for me to keep playing such a bland game, the campaign wasn't at all captivating. I don't like H6 very much, nor do I like 5 much either. H3 will forever be the best in the series with 4 having had a chance but was rushed and I feel somewhat incomplete, but it still has its charm!
Keep in mind that this game is designed to be very much so SINGLE PLAYER. It is balanced as such and you have to accept that you'll only be playing against AI and never a person. Provided that doesn't bother you, then this game is absolutely fantastic. There's a few minor bugs here and there but nothing serious and playing on impossible with each of the 3 classes working towards that 'no loss' ending is definitely something to make the game more difficult, just keep in mind you'll be wearing out your F5/F8 keys within the week

I love this game and am looking forward to the sequel and hopefully more sequels after that!