Yup, Heroes is free, unless you choose to buy heros/skins/mounts/etc. But when you play, even if you lose matches, you still get some in-game gold, and you can always buy heroes with in-game gold - so you never have to add to Blizzard's Duckberg Money Vault to get the character you want to play, you just have to play other characters (every week there are different characters you can play for free) until you save enough. This is how I play.
From a gameplay perspective, it's really easy to get into. I haven't played DOTA or LOL, but have played MOBAs that ran on Warcraft 3 and Starcraft 2, and it plays like those.
Things I like:
- Team shares leveling, instead of you having to level yourself
- The problem solving aspect of trying different strategies and character talent builds
- That matches are self contained, so each one is a fresh start, as opposed to something like WoW where you are perpetually trying to get to the next level. I can play 1 of 5 games, and they don't impact one another
Things I don't like:
- The occasional person that just has to tell me I am doing something wrong. /MUTED
- Not having more friends to play with so that we can develop strategies that work well on a team level