As a game, Runescape has a very poor reputation with gamers in general and MMORPG players in particular. In pretty much any MMO, "goback2RS" is a commonly heard insult for players who play that particular game poorly. The insult is generally based on the idea that Runescape is a relatively simple MMORPG, and that its player base is relatively young.
As I have noted many times before in my other articles, the development of Runescape is relatively unique. In the past decade the development of an MMORPG has become a multi-million dollar investment, and Runescape stands out as one of the few games that started out as the simple hobby of a pair of brothers. Even though Runescape has grown massively over the years, its relatively simple roots are still visible all over the game. Compared to the big money MMORPGs, Runescape seems to be incredibly simple. No races, no character classes, no large scale dungeons that require 20 or more players teaming up to clear them.
All in all, Runescape is indeed a lot simpler than most MMORPGs, but that's not necessarily a bad thing. The game is definitely more accessible, and several updates over the past few years have made the starting game incredibly welcoming to newcomers. This simplicity is definitely part of the reason why Runescape is so popular with a younger audience.
Of course, that's only part of the equation. The fact that Runescape can be played from your browser on pretty much any computer built in the past decade means that the game can easily be played from school or work. Furthermore, the game is incredibly cheap, requiring no initial financial investment and very low (and optional) monthly fees. Additionally, payment options like prepaid cards and telephone payments mean that players don't even need a credit card (or an adult relative with one).
But this is why players of other MMOs should actually be grateful for the existence of Runescape. While I don't have any exact figures, I think it is fair to say that a significant amount of all MMO players got their first contact with the genre through Runescape. Even if it isn't as grand or as flashy as other games are, Runescape is still a very good introduction to the genre. It can introduce players to all sorts of concepts that are unique to the MMORPG genre, such as the economy, the social interactions, team-based PvP on a large scale.
So is Runescape really "Baby's First MMORPG"? I suppose that in many ways it is, but that's definitely not a negative thing. Jagex have proven that they can cater well to their target audience, which consists both of younger players and of older players who are interested in a more relaxed MMO experience. It has survived in a time where many MMOs with starting budgets that rival the gross national product of most eastern European countries have failed to even get off the ground. It's baffling to me that MMO players still consider Runescape to be an insult to the genre, when many MMORPG developers could learn a lot from the game.