The meta-game is approaching stalemating as the best viable option in some match-ups. This is notoriously common in Barbarian vs Demon Hunter matches as when both players play safe, neither side can win, and when one player goes offensive, they usually lose. This is caused by a combination of very high mitigation and very high life regeneration. This can also be caused by players using low damage skills or weapons, but it is less common. The goal: no match should be endlessly indecisive while also allowing both sides a roughly equal chance of victory.
(2) Stale Moves
Currently, all classes have only one or two good offensive options and are forced to use certain defensive options to succeed in PVP. An example of this is the Barbarian's skill Rend: without it, they have virtually zero chance against most other classes. Another example is the Demon Hunter's skill Smokescreen, as there are zero viable strategies without this staple skill (which forces the DH to also use Preparation). The goal: all classes should have various offensive and defensive options which allow for a more diverse set of strategies and interesting matches.
(3) Class Balance
While it was announced that the game would be balanced around PVE, there is nothing preventing developers from implementing alternate mechanics within the PVP areas which has no effect on players outside of PVP. There are some classes which have little to no chance against other classes at the top. Wizard is an example of a class that needs an overhaul for PVP. Monks have a hard time against Demon Hunters, Barbarians have a hard time against Witch Doctors, etc. These match-ups could be addressed by altering various skills within PVP areas. The goal: no match-up is an excessively difficult uphill battle or ridiculously easy massacre.
(1) can be fixed by reducing life restoration from all sources or by reducing mitigation. (2) can be fixed by altering many existing skills in PVP areas to make them more attractive and increase diversity of builds. (3) can also be fixed by altering existing skills as well as existing mechanics, again only in PVP areas. (2) and (3) will also be less of an issue once team play is allowed as often teammates of different classes can compensate for a given class's weaknesses.
Again, this is not a rant but rather a constructive post. I would like to encourage other avid PVP brawlers/duelists to comment and suggest other ideas that developers can use to improve the system further.