I have been playing HoN since the early beta began. I never played DOTA or any other game like this before so the learning curve was pretty rough for me. It took about 20 games before I really felt that I had a good grasp of the basics (games take anywhere from 15-45 mins).
A few of the pros:
1. fast paced game
2. pretty good graphics
3. quite stable
4. great online play
5. TONS of strategies to use (offensive/defensive counters)
6. Lots of heros to pick from
7. Good friends lists, built in Voice servers etc. for fun times
1. Some people in the community are jerks just like any other online game
2. It can be hard to find a match to play with all of your friends on your team (people dont like to join games when they are all friends on one side since the scrub pick up groups usually dont know how to play together) Playing with 1-2 friends is pretty easy though, just not a full 5 man team.
In rebuttal to those who say the game is not balanced, there are really good balances in place to the game. If you think a character is overpowered, pick your hero late (at the end of the countdown) and wait to see what others pick. If you know the characters, there is a great counter character for everyone in the game. Also playing larger games with more players is easier to counter than a 2v2 or 3v3 game.