Wyatt Smith :
The biggest issue is that the characters are imbalanced to where the more expensive characters are quite a bit more powerful than the free or cheap characters. And by expensive, I mean they are ungodly expensive if you try to grind for them (expect 300 winning games or 500 losing ones), or expect to pay upwards of $20 per character.
Well, this is false...
1. No hero costs more than $9.99 in cash.
2. Some of the most competitive heroes are the cheapest ones. Valla and ETC are 2000g and simultaneously considered very well-balanced, even OP in the right hands.
1.) This was at the time of the beta when I was playing it. Thrall was the new character and was 15000 gold or $20 at the time. It sounds like blizzard corrected that part with the cash, but grinding would still take forever and a day (35 gold for a win, 20 gold for a loss).
2.) ETC must have came out after Thrall, so I have never tried him. Valla on the other hand can do high damage, but had no chance against Nova, Zeratul, or Thrall (10k for the other 2).
Nova and Zeratul were pretty much in permanent stealth mode except when attacking without any decent form of stealth detection against them. They could assassinate just about any character out there before someone could even react as they could be right on top of you and still not seen. As with Thrall, at the time he could basically 2va1 anyone on the map at half health and leave with 2 kills and full health afterwards.
With the 'cheap cost' characters, you had Raynor (which actually isn't too bad for cheap), Stitches (completely useless except for the chomp where you could carry an enemy inside your walls), the barbarian like character (again useless, pretty much on all fronts), and Valla (who may get decent kills, but her deaths will at least double them due to stealths insta-killing her).
Essentially, matches turned into one guy with the tank (has longer range than the towers), stealth guys protecting the tank (that essentially couldn't be targeted) or assassinating squishies (Valla, etc), and Thrall running around thrashing everyone else. Matches like that were over before they even started.
As I had mentioned, that was at the state when I was playing the beta (Thrall the new character). The game itself without those annoyances was quite fun, and I hope that they had corrected it.