Personally I don't believe that there are any
essential ingrediants for a good RPG. Different RPGs do different things and I've played RPGs that I consider good with various combinations of the ingrediants that you mention. However I'll have a crack at your ingrediants, one at a time, viewed entirely through the lens of my own, personal preferences.
DM/GM presence:
I've got no real opinions either way on this one. I think for a more traditional RPG then a GM is necessary but, equally, if a game is designed right then distributing GMing duties equally amongst the players can work absolutely wonderfully. I have equally high regard for WFRP, Nobilis and Polaris for instance. The first is very traditional, the second has such high powered players that, whilst the GM (or HG) has the traditional role, their powers are comparatively diluted and the third has no single GM with players taking on the role jointly in a round-robin style from scene to scene.
Character balance:
I do, personally, prefer things to be reasonably balance in a mechanical sense. It can be very boring if your character is massively incompetant compared to the rest of your group, especially in a more traditional game like D&D. Of course it doesn't always have to be that way and in games that lean further towards the pure roleplaying side of things (i.e. eschewing the tactical/strategic game side of the hobby to a greater or lesser extent) then mechanical balance becomes less of an issue. (Note: I'm not saying that D&D players don't 'roleplay,' I've played the game extensively and such claims are bollocks. I'm just saying that part of the fun of D&D and its ilk is the tactical side of gaming the system, something that you get short chamnged on if your particular character is mechanically weak through no fault of your own.)
Setting detail:
I prefer some setting myself. Nothing
too detailed though. Broad brush strokes that allow you to fill in details yourself tend to be more my thing. I'm not a fan of creating a home brew world totally from scratch, mostly because I'm lazy
. Equally too much setting can lead to feeling that your 'doing it worng' if you mess up setting details. That's not a very rational worry but ti is one that can crop up. Saying that I love WFRP
.
Randomisers:
Randomisers are usually desireable but not essential. As I mentioned earlier I'm a big fan of Nobilis, which is a purely resource management system. Mortal Coil seems to work in a similar way although I've not tried out the conflict rules in that in any meaningful way (the game I played in only had 2 conflicts, it was immense fun though!) Equally rolling dice is fun! (I prefer dice to drawing cards/whatever for purely aesthetic reasons.) Still, my luck with dice is legendarily poor so I'm, sometimes glad of the chance to ditch the randomness. It's usually fun though.
Social conflict mechanics:
I think I prefer my games with these to be honest. I don't like them to be too intrusive (an argument between characters or with an NPC shouldn't devolve into a dice roll immediately) but I think that they should be there. Otherwise you can easily end up with the problem of a back and forth argument between players where there's no incentive for either of them to give in and no mechanics to determine who wins or loses or, in some ways worse, you can get the problem that the loudest, most confident voice at the table gets to run the show. That isn't fair on the other players, period.
Genre:
Again I prefer my game to have some form of genre affiliation. I'm not a big fan of universal systems like GURPS (although I played Savage Worlds last week and the system seemed neat) but, equally, if the system works as a universal system with appropriate supplimental bolt-ons then fair play to it. I don't mind learning new systems for new games but some people like to stick to a single system and a universal system with genre/setting specific suppliments fulfills that need (plus the suppliments can be full of shiny goodness to steal for other games!)
Fantasy:
Fantasy isn't essential but there's a reason the the VAST majority of RPGs (and certainly all of the big, successful ones) contain elements of the fantastic. (Note: I'm not defining fatasy in terms of LotR, etc., alien visitations to an otherwise vanilla modern day Earth would count as having fantastical elements IMO.) It is those elements that help set the games apart from roleplaying your ordinary life. So, yes, fantastical elements are a desireable trait for me. On the other hand I had good fun playing Contenders the other day and that has no fantasy in it at all in the base game (although some might argue that it's closer to a card game with extra flavour but that's a debate for another thread.) Not only that but I could see a mob game or a straight historical game with no fantastical elements at all being great fun.
Strategic combat:
Again I think that this depends on the game. I think for more traditional RPGs then strategic combat is essential and damn good fun. However for certain indie games it is far less important and, whilst 'combat' occurs it doesn't appear in the traditional sense. Where combat and its outcomes are dictated by exactly the same system as is used to resolve any other conflict then strategy is largely irrelevant; it instead becomes all about setting the scene in a favourable manner and who has the most relevant traits/edges/whatever the hell you want to call 'em. So, yeah, depends on the game. I like both, depending on what mood I'm in.
Escalating player power:
I like my characters to grow and that growth to be refelcted in the mechanics. However that growth doesn't
necessarily have to correspond to my characters abilities increasing. In most games it does and indeed should (I don't know about you but I'd get pretty damn bored of running around as a lvl 1 D&D character forever) but if a game is designed for short term play of a few sessions then it's not relaly important. Indeed it can be fun to see your character deteriorate in the right game.
Visual aids:
Whilst not essential you can't really go wrong with some good visual aids. The most basic (and closest to essential) is to have a clean, well designed and
thematic character sheet. Past that props are always cool, who doesn't liek getting that note or map handed to them for real rather than just having it read out? Especially if it's been appropriately 'aged' or uses a relevant font or whatever. Minis are less relevant although well painted ones are always a nice addition and bloody useful in some games (D&D combat really is better with them an a battlemat, although you can play perfectly well without.)
So, in summary, I don't see any element as completely essential and different mixes of the different elements can produce some very good but very different gamers. Chalk me up as a fan of variety!