There have been several articles describing how a player of LoL feels once he enters into DotA 2 lately. The problem is those articles were written by people that didn't actually get into DotA 2 and they basically had no idea what they are talking about.
On the other hand, there are a lot of elitist statements by DotA veterans that act like douchebags calling LoL causal, kiddy, etc.
I played both of these games a LOT and I want to try to compare them without any prejudice and without stating which one of them is better.
Lets get this out of the way, the answer is known by most ppl anyway: LoL is more accessible than DotA 2. Dying is less punishing because you don't lose that much gold and even if you get owned two or three times during the laning phase you still won't be that much behind. If you get killed or are forced to run back to your base two or three times during the laning phase in DotA you are several levels and a lot of gold behind and it will be very tough for you to get back into the game. Also LoL has nice tutorials on everything, even video tutorials for every skill, etc. That is what makes it a lot more accessible.
Difficulty of both games depends on the skills of your opponents. DotA 2 is a bit tougher to get into, but that is a matter of accessibility, not a matter of difficulty.
3. Hero Design
I don?t aim to measure the artistic stylization of hero design, because its a matter of personal preference. I personally like both ways I like the wild colorful comics style of LoL just as much as I like the darker, more fairy tale-like approach of DotA 2. I want to focus more on character development, variability, etc.
3.1 Character variability
This is where DotA 2 kicks in. Despite having less characters than LoL, the roster actually gives you more options. Every single hero in DotA 2 is highly specialized in certain ways and lacking in others and each one has very unique play style. LoL has its greats too, but many of LoL champions feel a bit generic compared to the distinguished personality of DotA 2 heroes (I mean personality through skills and in gameplay).
3.2 Character development (through levels and items)
In both games, characters gain power through levels and through items. Level cap of champions in LoL is 18 and level cap of heroes in DotA 2 is 25. After the level cap is reached both games have their characters fully developed (i.e. you can?t have the same max level character with different skills). Level cap is a bit higher in DotA 2 not only by the numbers, it actually takes longer to reach it in-game. Thats why many DotA 2 players feel like they were stopped from growing just when they started to be a bit ahead of their enemies. Its also less punishing if you stay a few levels behind in LoL, because you will equate your opponents sooner thanks to the lower cap.
In terms of items, the difference is even bigger. It is almost impossible to max out on items in DotA 2 (i.e. get into a situation when you have plenty of gold and no idea what to buy to make your char better), while its quite common in LoL.
Its a tough call whether the overall lower power cap of characters in LoL is a bad thing. It allows for some nice comebacks of a team that slipped behind earlier in the game. On the other hand once your Sven is level 22 with BKB and Satanic in inventory and enemies are stuck around 18 struggling to gather their core items in DotA, you feel like a real badass.
Both games are heavily based on using hero skills. Some skills are very similar (like Amumus or Urgots ultimates vs Treants and Vengeful Spirits ultimates). Im not going to argue about who copies who. Its pointless and although all those skills were first used in DotA, some of them were designed by Guinsoo who later just used his own ideas again in LoL.
Its a matter of fact that overall skills are bigger in DotA 2. They cost more mana, have longer range, more damage, longer stuns or silence effects, etc. There are things like perma invisibility, 5sec. stuns, etc. Therefore it is more important to use them right. Missed a fissure? You are out of mana and will be for some time unless you buy some mana regen items or go back to your base!
On the other hand, it is more satisfying to score a kill in DotA 2, because not only it matters more (kills make more difference in DotA 2 than in LoL), but it also comes with a bigger bang!
On first sight both maps look basically the same (which is also what most anonymous LoL players say about them because they never seriously played DotA 2), but in a closer look, there is a lot of difference.
First of all, the top lane is vastly different from the bottom lane in DotA 2. Each side has one lane, that allows pulling of creeps to neutral camps (gaining more XP by killing neutral camps early and denying some XP to your opponent because the neutrals kill some of your creeps in the process), but it is also much easier to gank this lane (where a jungler usually is if the team decides to have one).
What I love about LoL map is that it contains neutral camps with various bonuses. Timing respawn of those camps adds great dynamic to the game and forces shodowns. DotA basically only has Roshan and it is not that crucial to kill him as soon as he spawns.
There are also some other differences between the maps like high grass vs high grounds that prevent vision, etc., but those are minor in my opinion.
Its also worth to mention the fact that LoL has a 3v3 map Twisted Treeline, which is great if you only have two friends to play with currently online. I personally only play TT in LoL lately, because when Im alone or if we are five, I go for DotA 2.
Both games are great at what they are doing.
LoL is more accessible, while DotA 2 is more punishing, but also more rewarding. LoL is easier to learn, DotA 2 is a deeper and more complex experience.
If you want just to have fun and relax in a game of this genre, go for LoL, you will have tons of fun. If you have group of 5 people with similar mindset - thats even better, you're gonna have even more fun!
If you want a game that you need to put a lot of effort into to really master, if you have 4 reliable friends to make a team with and if you want to be rewarded for your hard work by real excitement of well deserved victory, go for DotA 2. It will take you on a journey through hell, you will be owned hard by teams that play tighter, gank better, and every little mistake will cost you the game. But beating the other team, punishing their own mistakes and breaking through their base will be huge satisfaction and feeling of accomplishment!