Here's some food for thought...
If you see certain heroes and strategies, and skill spamming over and over then you might want to take a closer look at why. In my experience, competitive gamers tend to gravitate what works the best while being the easiest to consistently execute.
So, if after a while you mainly just see tower rooks to the exclusion of other builds, then you have to consider that might be an internally overpowered line. Or, conversely other internal rook builds might be underpowered. At any rate, if a pattern establishes, then you have to at least consider things might be out of balance.
Additionally, if game after game you see a preponderance of Erebus and Unclean beast players then you have to look closely at those two classes.
I still think it's too early to tell. Only after all the MP issues are worked out and we have a meaningful pantheon database will you be able to start to make better judgements.
My feeling is that Spit as a spell is a little too good but I might be wrong about that. But I only say that for casual unorganized play. But as I've seen it, it seems to be spammable, low cooldown, high damage and it is used alot w/ the UCB not risking much to employ it.
This is a game that seriously leverages team work and I think that in the long run winning teams will be well coordinated ones and so individual hero balance will probably take a back seat to synergies between classes and I except there will be some combos that will need a serious look.