The issue I have with Dota (2) IN CONTRAST to League of Legends is that, taking a page from some developers, Dota (2) has a LOT of anti-fun.
Anti-fun? Basically things that simply detract FUN from the player, whether it be usability, balance, or even aesthetics. The two have lots of different design philosophies in terms of balance, so while there are places to touch on in terms of balance issues, it's core intents are different.
Now, any action 'creates' fun and anti-fun. Leveling up and choosing skill points? A little bit of fun. Beating up another person? Lots of fun. But at the same time, these actions detract fun from the other players in a multi-player setting. If you gave one guy the BEST GUN THAT KILLS ANYONE EVER, I'm sure one guy would have some fun, while everyone else wouldn't. Now, it becomes an issue of creating design [balance, usability, aesthetics] that manages to keep things fun for one person and less overall anti-fun for everyone else.
Dota originally started off as a haphazard mod that slowly grew into something amazing, but led by people who literally just wanted to add COOL stuff, DISREGARDING balance, although naturally they touched on it. This is a large part of Icefrog's [one of the original/major Dota allstars developer and a major dev on Dota 2] design philsophy, and led to a lot of fun BUT negative stuff in dota - burden of knowledge, little counter play, etc.
LoL manages to do its OWN thing and really try to keep things FUN and BALANCED with as little anti-fun as GENERALLY possible. Dota 2? NOTHING. It doesn't advance, it doesn't innovate, it doesn't reduce anything. And not only that, every single bit of anti-fun comes along with it.
For random examples off the top of my head that I can remember...
WHY DO YOU HAVE A PICTURE OF YOUR KILLER LAUGH AT YOU WHEN YOU DIE? This is a design choice that makes the PLAYER feel bad with absolutely no fun derived to the guy who defeated you. I mean, he KNOWS you're being laughed at, but he's more likely off a high on KILLING you and paying attention to objectives, while for 20-60 seconds some guy is laughing at you to make you feel worse. THIS IS NOT A DESIGN CHOICE THAT IS FUN. If NOTHING else, this needs to be a toggle/option/setting.
Controls. Good fun/anti-fun generally derives from CHOICES. I DID something, and whatever happens is the result of something I AFFECTED. Not because I'm using overpowered characters, not because I didn't read each and every description/skill/hero a thousand times and memorized. Given the same scenario, resources, and etc., I beat someone with my OWN SKILL. Dota genre is a multiplayer game, and it TAKES ADVANTAGE of that in a rather novel way. ON THE CONTRARY, Dota(2) doesn't really do this much. It relies on burden of knowledge, edge cases and abuse cases, hard counters, and LOTS of mechanics. There is respect for those that do these (namely mechanics) well, but... there's a lot of things that sorta neuter choices. That said, there is a lots of DEEP and hardcore fun to be had, but... a lot of it relies on EXCESSIVE knowledge, which isn't always the best design choice to put, and more on mechanics over choices, which isn't the best utilization of the genre. Let those that have deep mechanics shine, not make it a requirement to play.
Aesthetics. Massive bias atm, since I'm following it from Lol's point of view, but it lacks a lot of things that make important stuff stand out. Things can be shown better, the color coding for champions is not immediately obvious (various colors of champs bars/thingey on top of the screen vs red and green).
Control scheme needs work. It's something you get used to, but it ISN'T immediately obvious and requires a LOT of controls that you, again, HAVE to learn to be proficient. It's not like everything needs to have only two buttons, but the MORE you add the HARDER it is for the player to get to the meat of the game: choices and having fun.
Etc.
Dota 2 didn't invent, innovate, or reduce anti fun. It's just a graphics upgrade with some various misc/control scheme on the side. It does some stuff better, and naturally has a LOT of polish. BUT. It doesn't use the MOBA genre in the FUNNEST way, nor does it attempt to. Combined with its issues, it's not a game I can keep playing.
that said I have such massive LoL biased that this entire post need be taken with a grain of salt.