Heroes of the Storm is a MOBA created by Blizzard Entertainment
Pro Hero and playstyle diversity
Blizzard has gone above and beyond to introduce Heroes that break the standard molds for Tanks/Support/Damage characters. The talent system allows for diversity in how a character plays, even if they are considered Support, they can go for damage or utility. Each Hero has 2 Heroic Abilities(Ultimates) providing even more diversity in how each character can be played. Also, Blizzard has introduced several unique heroes, like Lost Vikings: which are 3 heroes in one, and can be controlled separately; Also, newly added Cho'Gall, which required 2 people to control 1 hero.
Pro Shorter game times
Decreasing the importance of "laning" and increasing team fights and map objectives. Also, many map objectives keep the games to time limits between 15 - 30 minutes. Much more manageable for people not able to commit an hour to one match. AI games are even shorter.
Pro It's always possible to make a comeback
Even if you are in trouble because you lost almost all the game, you can still win by killing the enemy team on a stupid move they made at the end of the game. And it's never unfair: it's always because the losing team was overconfident and the winning one was the focus.
Pro No last hitting, no gold, no items
The game does away with the shop mechanic entirely. No last hitting means players don't have to focus on a minigame for the first 20 minutes so they can jump into the action much faster. No shop means that supports aren't starved for cash and can remain strong and relevant throughout the game. No items allow for the hero-specific talent system to shine, which provides a much more unique and easily balanced way to enhance your character.
Pro Deep but not complex
The game removes a lot of pointless features of other games like last hitting and out-of-game rune/card buffs. It's also much clearer, with natural percentage based increases for characters rather than "armor/intelligence" stat increases. It also has a large map pool with greatly differing objectives in each one forcing you to consider how your playstyle will adapt to the opponent and the map itself. It may appear to be simple, but there is a lot of hidden depth.
Pro Easy to learn
Heroes of the Storm was created to be a streamlined, modern take on a MOBA, something that many others have aimed for but HotS succeeds in. Shared XP keeps teams leveling together; No Last Hits means that everyone gets XP from minions and puts less importance on who gets the kill, since there is no Carry-player. Choosing talents instead of having to buy items gives the game complexity without forcing players to wade through menus and travel back to base. The game still offers a challenge to master at higher levels, but is more accessible to new players.
Pro Fun emotes from heroes upon team work and team kills and more
If you play Nova and Kill Vala, Nova will say "HUNTER!?!? more like Hunted!!"
Or if you play support and heal Raynor he will say "This medic is my new best friend".
These emotes make it very clear what happened, and add a dimension of fun that you don't see in other MOBAs.
Also you can hear some emotes after other events, like your own hero death/respawn or during starting second of the match.
Con Slow fights
Heroes inflict little damage to each other, which has the potential to make fights seem long. On top of this when one falls behind many of their skills will become useless making for a fight that one is delegated to a support role, which will also add to the slow feeling of a fight.
Con Terrible matchmaking
In any of the matchmaking queues, the chance of being put against someone with much higher skill than yourself is very high. The ranking system goes in this order: Bronze, Silver, Gold, Platinum, Diamond, Master, Grandmaster. On multiple occasions, silver players have been placed against an entire team of Grandmasters with bronze allies, leading to very poor experience.