Their games tend to lack depth, complexity, and maturity, especially in storytelling.

When did I say "working" was an "indicator" of being the "best"? The working part of the game is one of the first step which many developers already fail at but there are other reasons of course. Nintendo is the best developer out there imo because their games have been consistant in terms of quality and polish  which can't always be said for a lot of other developers. If you think there is a better developer out there that have as much consistancy as Nintendo when developing games, then great but imo (which is the key here cause it is an opinion), they are the best

If we acknowledge that their games do lack complexity and maturity (like your reply hints) then we can conclude that while it isn't a problem per se, Nintendo lacks variety as they don't develop these kind of titles for these kind of audience. Hence, we can safely conclude they're not the best videogame developers of all time, as they haven't dare develop in these realms. :P

Well, in one point, nintendo could improve things, that is on theirs moderns tutorials approach. I see a lot of people complaining about games padding out too much, those mario&luigi rpgs specially. I get, they want the world to see their quirckness and all, but after the 5th entry, you are satisfied and want to jump directily to gameplay.
Their netcodes could be better too, a lot of people complain about been kicking from lobbies in MK8, itens going missing, etc.

The questio is, one thing is saying that nintendo is not perfect, that what i said here implies. The other is saying that they are not the best. That implies there is a better one. In recent memory, the possible contenders could be nautghy dogs, blizzard and valve, at least from what i heard.

Is nautghy dog better than nintendo? In the net code department, yes, from what i heard. Their games from ps1 were fun too, i actually enjoyed crash more than mario 64. But, they have their shares of no so much good games too. From what i heard, the first uncharted is not really good, but i don't know if their games in the PS2 era were actually good. I only heard from them in the HD era, they were pretty overshadowed by santa monica and japan studios on that era, i dare to say. Their decisions to put microtransactions on a 60 dollar game was also not meet with a smile on the community. But i do believe that crash, uncharted 2 and last of us will be seem as classic in 10+ years. I fon't know if their games are as much polished as is nintendo games, i will let for you too decide. But if someone that played both companies games say yes, them naugth dog wins. For me, toutgh, the microtransaction balance the net code, so i would call a tie.

Next: blizzard. Well, i played warcraft 3 and think it is a fantastic game. I played a lot of dota in their custom maps, but also played anotheer custom match too and are all really good. Diablo was also a great franchise and people had a lot of positive things to say about it. Not only that, but diablo 2 recieved pacths for more than 10 years! They were really commited to polish the game for year and year, and provide actual support to the costumers. Besides, their net code was really impressive, with starcraft working with hundreds of units moving in the early 00's on internet. They also created a great experience that would grow to go be as big that all other companies would go after a slice of it. I'm talking about WoW. Like it or not, the game gathered a impressive fanbase, and outlived any competitor that tried to step in that space. I would call it a win, but them since starcraft 2, things were not so shinny in their lands. Starcraft 2 made difficult for custom maps to work, and people started complaining and the game was bad. Them, diablo 3 came and it was a disaster. Not only in the online aspects, but even after that got working, a lot of people were disapointed with the game, that even now some are not happy with. HoS seem to be on the trace to be well accepted by the comunity (those not so much into MOBAs), and heartstone is really working out well for them. Even if WoW is finally losing momentum, blizzard seems to be back on their tracks, with game like overwatch looking promissing. Yet, i think that nintendo never was in bad position as bad as blizzard once was. so i give them the edge on this one.

Now valve. Another company that usually do the best games of all time for some. People are still impressed with half life, one game that most people say was never surpassed in the fps genre. Expect for, maybe, another valve game, portal. This are the single player games, but left 4 dead is also a very well recieved game. As far as their net code goes, well, thei intend to offer much, but as someone who plays dota 2 in a daily basis, the is a lot of room for improvment, specially in the stability space. That is probably the biggest problem that i find in their games: some can be really rough on the edges at launch. Even if dota 2 is much better now, it still hundred of know bugs for years now, even when they had 2 years of beta testing. Not only that, but almost every match see someone disconnecting for no apparent reason, etc. CS: GO recieved a lot of criticsim at launch too, but now is getting beter. I would question theirs method for introducing new player too. So, for me, nintendo wins this one too.

So, here it is. I thin the only one that can be better than then are ND, all thing considered. But since i don't play as much nintendo games since the 64 and some in the NDS, and even a lot of blizzard/valve and ND i never played, i will let someone who played them to say what do they think.

And Xeno, and Fire Emblem

I don't know for sure if they are the best developers but I can say for sure that they are the smartest developers. Being able to develop fun games that million would buy while keeping budget in range isn't something that every developers do.

Mmmm, maybe it's just me, but I generally find Nintendo games just good. Nothing outstanding, nothing superb; but they ain't bad either. I don't know about the unique thing or the "Nintendo feel", though.

Well, Fire Emblem is very mature in tone and has a lot of depth. Monolith Soft is Nintendo so I put it out there for anyone to take or leave. Also, the discussion to this point was about Nintendo as a whole. We should not sell them short. Maturity and depth in story and gameplay CAN be found in Nintendo IPS. 

Universally, they are not. But any of those three are a reasonable metric that they fall on the low end of, especially when it comes to the stories they put in their games. Other developers have used those facets of design to create unique experiences.

I think Nintendo is creative and has made some of the most iconic characters of all time. However, i think they lack diversity and hug the family friendly title too much. They especially lack in the story department. Where Nintendo makes solid games in certain genres, they also lack in many others.