Only enjoyable if you mute the entire population or only run premade groups. Don't waste your time.
I have played dozens of competitive FPS games - TFC, TF2, CSS, Tribes, and many others for hundreds of hours. I have played half a dozen MMOs for hundreds of hours. I have played my fair share of XBL as well. I will say I have never come across a gaming community so toxic and openly hostile towards new players. I played a handful of bot matches (against NPC opponents) and literally every match was trolled and insulted until I left. For every helpful player (I'm assuming they exist even though I have never met one in game) there are dozens and dozens of feral 13yo sociopaths who are openly hostile towards any newcomers. The equation for this game: highly competitive players + long matches + high teamwork requirement + free to play = an unbelievable amount of rage and griefing. This game is literally a rage-engine.
In terms of gameplay DOTA2 is like pretty much any other MOBA. If you have played LoL, HoN, or RoI you should have an idea of how the game plays for the most part. The visuals are better than other entries in the genre and because it is a Valve game it has full Steamworks integration and everything associated with that. I will say that I like the look and style of the heroes a lot more than other MOBAs and each has their own unique animations.
Tutorial is pretty much useless and only covers the bare minimum for being able to play the characters. Any kind of strategy or advanced tactics you still need to read articles or watch endless YouTube videos. Not that it matters much, if you are new you will be relentlessly griefed anyway. They added a mentor and community based training program to TF2 a year or more ago and this game DESPERATELY needs something like that.
I really can't understand Valve's angle on this game. I'm sure the microtransaction stuff will basically be a license to print money, but they have always been about community support. With such a toxic community inherent in MOBAs its going to start rubbing of on their brand if they are not careful. Ever since beta started the majority of players have been openly hostile towards new people. And since the game has been in beta so long the amount of rage being directed by the vets towards all the new people just starting out is beginning to reach critical mass and will completely turn new players off playing in the future.
If you have not played a MOBA before save yourself a lot of disgust and just don't even bother downloading it. If you have played MOBAs previously, you know what you are getting into and besides visuals and Valve's name there is nothing that makes it any better than the ones already available.