I played a lot of Dota and Dota 2. Reasons why I played a lot:

1. You are playing against other people. So no scripted AI.

2. You can build your heroes in the way you want and how you see fit. Even though you only have 4 skills, what you focus on as you level up determines your game.

3. Lots of item combinations adds another layer to your hero development.

4. Different teammates with different heroes produce different games. So almost no two games can be identical.

5. You noticed your skill comes and goes. You had your moments, and you also had your losses. It baffled you why you kicked ass 5 games ago, and suddenly got owned.

6. And finally, those critical moments that could suddenly turn the tide of the game makes it all worth it. Your team is losing grounds, but suddenly that one ultimate executed at the right time killed all your opponents heroes, and you all rushed to their base and destroy their hall with few HP left.

I believe all these are called 'horizontal' design.

MMORPG, however, is very 'vertical'. You have a fixed set of choices (hero/skills), and you explore them by playing more, level up more, get better items, explore harder dungeons.

MOBA is horizontal. All items are available up front as long as you have the coins. You likely max out your hero in every game, or get very close to it.

If by MMORPG you mean World of Warcraft, then perhaps.

I wouldn't say MOBAs are horizontal, they still (usually) have levels and in most of the cases you have to level up to be able to use better spells or skills, like the ultimate in Dota, LoL e.t.c. Besides, most of the MOBAs have fixed choices in terms of spells and skills anyway.

That's why these abbrevations don't help much, they're too broad and you can't draw many conclusions from them.

The failure rate for Moba's and MMORPG's is very high, so I wouldn't call them successful genres.

The ones that succeed seem to succeed based on constant updates, community involvement, and established franchises.

That. Pretty much 100% agreed.

So many MMORPG failures in the last 10 years its not even funny. I wouldn't call a genre where most games that are developed as premium / sub-based have to turn into free-to-play within mere months of their releases as "successfull".

The MOBA Space just lacked competition until now. With HotS and Blizzard entering that space, I guess many others will follow. And we will see yet again the same same churn of newcomers failing again and again save the ones that use proven brands (like Blizzard) and maybe fresh gameplay concepts to at least keep their games profitable for a while.

The one reason why WoW was able to keep afloat fo so long is simple. It was there when there was demand for a new MMORPG, it used a known brand to attract people (WC3 was all the rage at that time), and it had a quite well executed world at the time. Like facebook, its success was fuelled by a combination of sheer luck (being there at the right time) and some clever decisions... as soon as it had a certain critical mass, success fueled success. Old blood will not leave WoW as they have invested too much into it already, new blood will still pour in as there are so many existing players, making the virtual world more alive and giving a lot of community word-of-mouth free advertising power to the game.

But as conquestor said, Blizzard DOES invest a lot into upgrades and expansions. As much as I am NOT a blizzard fan, they DID grow the game considerably in the years of its existence. They are actively working on keeping their cash cow alive.

Coming back to Conquestors comment, I'd say at the moment one of the biggest "successfull genres" seems to be the arcade-sim, especially arcade-tank-sims like WoT. With Warthunder having released a Tank expansion and Armoured Warfare having moved into OB, there are now 3 competitors in a space that was vitrually non-existent 5 years ago, and many considered to be niche (real tank-sims, like all simulators, ARE extremly niche after all).

I don't think games in this genre will ever reach certain MMORPG or MOBA genre game like levels of success, but at least it seems that there is still growth in the playerbase in this genre whereas the MMORPGs and MOBAs must have reached their zenith long ago.

All comes down how you define success. Do you define it by currently active players (MMORPG are still strong there, as are MOBAs)? A growing user base (most probably no for both, even with HotS)? Successes in the E-Sports community (no for MMORPGs, yes for MOBAs)? A lot of successfull games (no for both, both are dominated by about 1-3 very successfull titles)?

Just looking at WOWs, yes, MMORPGs seem to be successfull (which led to everyone and their dog working on an MMORPG in the late 2000-noughties and many millions of dollars being lost in these projects).

Just looking at LoL and Dota MOBAs seem to be successfull (leaving out the fact that they are just extremly visible thanks to E-Sports and just much more accessible to play for many than for example MMORPGs because of short matches versus yearlong grinds).

Survivorship bias. Look at the failed examples to measure success, not at the successfull ones.

Then there is the question: why looking for successes? what do you want to read out of success? If you want to find out if you should move into a space because others seem to have a lot of success doing it, then you are doing things backward. That is the false assesment of the situation that led to all these failed MMORPGs more than bad execution. Trying to compete with a monopoly like WoW has it at the moment in the MMORPG space is a battle even big studios cannot win.

Best to wait for its inevitable death (at some point, even the most loyal player will loose interest and the game will just not look attractive enough to new players), and the time when the MMORPGs star is sinking again and it is not called a "successfull genre" anymore... THEN the MMORPG genre is ready for a new contender which might enjoy the same success WoW is doing now (IF this new contender is able to adapt to the new times, and does offer a new and improved MMORPG formula).

MMORPG and MOBA are completely different.

MOBAs have two teams of players, each controlling an RPG-esque hero, fighting for map control, usually pushing back and forth along "lanes" populated by NPCs. There's a well defined structure to each match with a winning team and a losing team.
They grew out of Starcraft and Warcraft 3 custom maps, with DOTA being the most famous. Tower defense maps were basically the breeding grounds that MOBA maps grew out of.

MMORPGs are an RPG with a massive number of players able to interact at one time, such as standing in the same place. MMO's typically have no end, and no way to win (but will have quests or PvP events of different kinds, which act as mini-games with winning/losing).
They may have MOBA-style games within them, but thats unrelated -- they could have an FPS minigame inside them, but that doesn't suddenly make FPS's and MMORPG's the same thing...

There actually has been a large number of MOBAs and MMORPGs over the years, but we only think of a few of them because the majority of these games fail horribly.

Thanks for the insights, this helps a lot to get a good overview.

I'm widening my knowledge on game design and recently entered the world of RPG's, that was the trigger behind the original question. Currently working my way through "Swords & Circuitry, designers guide to computer RPGs.